Merge branch 'siri/logger-fix'

* siri/logger-fix:
  Update documentation of logger and error_logger
  Change type name logger:log() to logger:log_event()
  Update preloaded
  Update primary bootstrap
  Rename module logger_simple to logger_simple_h
  Change env var logger_log_progress to logger_progress_reports
  Remove HandlerId from handler callback functions and add it to Config
  Change handler id for sasl handler from sasl_h to sasl
  Change Compare parameter to logger_filters:domain/2
  Update Logger documentation
  Rename reset_module_level to unset_module_level
  Allow chars_limit to limit strings
  Add logger:update_formatter_config/2,3
  Set legacy_header=true for kernel's default handler only
  Improve documentation of logger and error_logger
  Use system_time instead of monotonic_time as timestamp in logger

10 files changed, 1398 insertions, 855 deletions

diff --git a/lib/kernel/doc/src/error_logger.xml b/lib/kernel/doc/src/error_logger.xml
index c9fe9484e4..f418aa5bbe 100644
--- a/lib/kernel/doc/src/error_logger.xml
+++ b/lib/kernel/doc/src/error_logger.xml
@@ -33,44 +33,35 @@
   <description>
 
     <note>
-      <p>In OTP-21, a new API for logging was added to Erlang/OTP. The
+      <p>In Erlang/OTP 21.0, a new API for logging was added. The
 	old <c>error_logger</c> module can still be used by legacy
-	code, but new code should use the new API instead.</p>
+	code, but log events are redirected to the new Logger API. New
+	code should use the Logger API directly.</p>
+      <p><c>error_logger</c> is no longer started by default, but is
+	automatically started when an event handler is added
+	with <c>error_logger:add_report_handler/1,2</c>. The <c>error_logger</c>
+	module is then also added as a handler to the new logger.</p>
       <p>See  <seealso marker="logger"><c>logger(3)</c></seealso> and
 	the <seealso marker="logger_chapter">Logging</seealso> chapter
-	in the user's guide for more information.</p>
+	in the User's Guide for more information.</p>
     </note>
 
     <p>The Erlang <em>error logger</em> is an event manager (see
       <seealso marker="doc/design_principles:des_princ">OTP Design Principles</seealso> and
       <seealso marker="stdlib:gen_event"><c>gen_event(3)</c></seealso>),
-      registered as <c>error_logger</c>. Errors, warnings, and info events
-      are sent to the error logger from the Erlang runtime system and
-      the different Erlang/OTP applications. The events are, by default,
-      logged to the terminal. Notice that an event from a process <c>P</c> is
-      logged at the node of the group leader of <c>P</c>. This means
-      that log output is directed to the node from which a process was
-      created, which not necessarily is the same node as where it is
-      executing.</p>
-    <p>Initially, <c>error_logger</c> has only a primitive event
-      handler, which buffers and prints the raw event messages. During
-      system startup, the Kernel application replaces this with a
-      <em>standard event handler</em>, by default one that writes
-      nicely formatted output to the terminal. Kernel can also be
-      configured so that events are logged to a file instead, or not logged at all,
-      see <seealso marker="kernel_app"><c>kernel(6)</c></seealso>.</p>
-    <p>Also the SASL application, if started, adds its own event
-      handler, which by default writes supervisor, crash, and progress
-      reports to the terminal. See
-      <seealso marker="sasl:sasl_app"><c>sasl(6)</c></seealso>.</p>
-    <p>It is recommended that user-defined applications report
-      errors through the error logger to get uniform reports.
-      User-defined event handlers can be added to handle application-specific
-      events, see
-      <seealso marker="#add_report_handler/1"><c>add_report_handler/1,2</c></seealso>.
-      Also, a useful event handler is provided in STDLIB for multi-file
-      logging of events, see
-      <seealso marker="stdlib:log_mf_h"><c>log_mf_h(3)</c></seealso>.</p>
+      registered as <c>error_logger</c>.</p>
+    <p>Error logger is no longer started by default, but is
+      automatically started when an event handler is added
+      with <seealso marker="#add_report_handler/1">
+	<c>add_report_handler/1,2</c></seealso>. The <c>error_logger</c>
+      module is then also added as a handler to the new logger,
+      causing log events to be forwarded from logger to error logger,
+      and consequently to all installed error logger event
+      handlers.</p>
+    <p>User-defined event handlers can be added to handle application-specific
+      events.</p>
+    <p>Existing event handlers provided by STDLIB and SASL are still
+      available, but are no longer used by OTP.</p>
     <p>Warning events were introduced in Erlang/OTP R9C and are enabled
       by default as from Erlang/OTP 18.0. To retain backwards compatibility
       with existing user-defined event handlers, the warning events can be
@@ -99,6 +90,9 @@
           The function returns <c>ok</c> if successful.</p>
         <p>The event handler must be able to handle the events in this module, see
           section <seealso marker="#events">Events</seealso>.</p>
+	<p>The first time this function is called,
+	  <c>error_logger</c> is added as a Logger handler, and
+	  the <c>error_logger</c> process is started.</p>
       </desc>
     </func>
     <func>
@@ -108,37 +102,40 @@
         <p>Deletes an event handler from the error logger by calling
           <c>gen_event:delete_handler(error_logger, <anno>Handler</anno>, [])</c>,
           see <seealso marker="stdlib:gen_event"><c>gen_event(3)</c></seealso>.</p>
+	<p>If no more event handlers exist after the deletion,
+	  <c>error_logger</c> is removed as a Logger handler, and
+	  the <c>error_logger</c> process is stopped.</p>
       </desc>
     </func>
     <func>
       <name name="error_msg" arity="1"/>
       <name name="error_msg" arity="2"/>
       <name name="format" arity="2"/>
-      <fsummary>Send a standard error event to the error logger.</fsummary>
+      <fsummary>Log a standard error event.</fsummary>
       <desc>
-        <p>Sends a standard error event to the error logger.
-          The <c><anno>Format</anno></c> and <c><anno>Data</anno></c> arguments
-	  are the same as the arguments of
+        <p>Log a standard error event. The <c><anno>Format</anno></c>
+          and <c><anno>Data</anno></c> arguments are the same as the
+          arguments of
 	  <seealso marker="stdlib:io#format/2"><c>io:format/2</c></seealso>
-	  in STDLIB.
-	  The event is handled by the standard event handler.</p>
+	  in STDLIB.</p>
+        <p>Error logger forwards the event to Logger, including
+          metadata that allows backwards compatibility with legacy
+          error logger event handlers.</p>
+	<p>The event is handled by the default Logger handler.</p>
+	<p>These functions are kept for backwards compatibility and
+	  must not be used by new code. Use the <seealso marker="logger#macros">
+	    <c>?LOG_ERROR</c></seealso> macro or
+	  <seealso marker="logger#error-1"><c>logger:error/1,2,3</c></seealso>
+	  instead.</p>
 	<p><em>Example:</em></p>
         <pre>
-1> <input>error_logger:error_msg("An error occurred in ~p~n", [a_module]).</input>
-
-=ERROR REPORT==== 11-Aug-2005::14:03:19 ===
+1> <input>error_logger:error_msg("An error occurred in ~p", [a_module]).</input>
+=ERROR REPORT==== 22-May-2018::11:18:43.376917 ===
 An error occurred in a_module
 ok</pre>
         <warning>
-          <p>If called with bad arguments, this function can crash
-            the standard event handler, meaning no further events are
-            logged. When in doubt, use
-	  <seealso marker="#error_report/1"><c>error_report/1</c></seealso>
-	  instead.</p>
-        </warning>
-        <warning>
           <p>If the Unicode translation modifier (<c>t</c>) is used in
-            the format string, all error handlers must ensure that the
+            the format string, all event handlers must ensure that the
             formatted output is correctly encoded for the I/O
             device.</p>
         </warning>
@@ -146,36 +143,51 @@ ok</pre>
     </func>
     <func>
       <name name="error_report" arity="1"/>
-      <fsummary>Send a standard error report event to the error logger.</fsummary>
+      <fsummary>Log a standard error event.</fsummary>
       <desc>
-        <p>Sends a standard error report event to the error logger.
-          The event is handled by the standard event handler.</p>
+        <p>Log a standard error event. Error logger forwards the event
+          to Logger, including metadata that allows backwards
+          compatibility with legacy error logger event handlers.</p>
+	<p>The event is handled by the default Logger handler.</p>
+	<p>This functions is kept for backwards compatibility and
+	  must not be used by new code. Use the <seealso marker="logger#macros">
+	    <c>?LOG_ERROR</c></seealso> macro or
+	  <seealso marker="logger#error-1"><c>logger:error/1,2,3</c></seealso>
+	  instead.</p>
 	<p><em>Example:</em></p>
         <pre>
 2> <input>error_logger:error_report([{tag1,data1},a_term,{tag2,data}]).</input>
-
-=ERROR REPORT==== 11-Aug-2005::13:45:41 ===
+=ERROR REPORT==== 22-May-2018::11:24:23.699306 ===
     tag1: data1
     a_term
     tag2: data
 ok
 3> <input>error_logger:error_report("Serious error in my module").</input>
-
-=ERROR REPORT==== 11-Aug-2005::13:45:49 ===
+=ERROR REPORT==== 22-May-2018::11:24:45.972445 ===
 Serious error in my module
 ok</pre>
       </desc>
     </func>
     <func>
       <name name="error_report" arity="2"/>
-      <fsummary>Send a user-defined error report event to the error logger.</fsummary>
+      <fsummary>Log a user-defined error event.</fsummary>
       <desc>
-        <p>Sends a user-defined error report event to the error logger.
-          An event handler to handle the event is supposed to have been
-          added. The event is ignored by the standard event handler.</p>
+        <p>Log a user-defined error event. Error logger forwards the
+          event to Logger, including metadata that allows backwards
+          compatibility with legacy error logger event handlers.</p>
+	<p>Error logger also adds a <c>domain</c> field with
+          value <c>[<anno>Type</anno>]</c> to this event's metadata,
+          causing the filters of the default Logger handler to discard
+          the event. A different Logger handler, or an error logger
+          event handler, must be added to handle this event.</p>
         <p>It is recommended that <c><anno>Report</anno></c> follows the same
           structure as for
 	<seealso marker="#error_report/1"><c>error_report/1</c></seealso>.</p>
+	<p>This functions is kept for backwards compatibility and
+	  must not be used by new code. Use the <seealso marker="logger#macros">
+	    <c>?LOG_ERROR</c></seealso> macro or
+	  <seealso marker="logger#error-1"><c>logger:error/1,2,3</c></seealso>
+	  instead.</p>
       </desc>
     </func>
     <func>
@@ -192,37 +204,40 @@ ok</pre>
 	    is <seealso marker="kernel_app#deprecated-configuration-parameters">
 	    deprecated</seealso> since
 	    the <seealso marker="logger">Logger API</seealso> was
-	    introduced in OTP-21. The variable, and this function, are
-	    kept for backwards compatibility since they still might be
-	    used by legacy report handlers.</p>
+	    introduced in Erlang/OTP 21.0. The variable, and this
+	    function, are kept for backwards compatibility since they
+	    still might be used by legacy report handlers.</p>
 	</note>
       </desc>
     </func>
     <func>
       <name name="info_msg" arity="1"/>
       <name name="info_msg" arity="2"/>
-      <fsummary>Send a standard information event to the error logger.</fsummary>
+      <fsummary>Log a standard information event.</fsummary>
       <desc>
-        <p>Sends a standard information event to the error logger.
-          The <c><anno>Format</anno></c> and <c><anno>Data</anno></c> arguments
-	  are the same as the arguments of
+        <p>Log a standard information event. The <c><anno>Format</anno></c>
+          and <c><anno>Data</anno></c> arguments are the same as the
+          arguments of
 	  <seealso marker="stdlib:io#format/2"><c>io:format/2</c></seealso>
-	  in STDLIB. The event is handled by the standard event handler.</p>
+	  in STDLIB.</p>
+        <p>Error logger forwards the event to Logger, including
+          metadata that allows backwards compatibility with legacy
+          error logger event handlers.</p>
+	<p>The event is handled by the default Logger handler.</p>
+	<p>These functions are kept for backwards compatibility and
+	  must not be used by new code. Use the <seealso marker="logger#macros">
+	    <c>?LOG_INFO</c></seealso> macro or
+	  <seealso marker="logger#info-1"><c>logger:info/1,2,3</c></seealso>
+	  instead.</p>
 	<p><em>Example:</em></p>
         <pre>
-1> <input>error_logger:info_msg("Something happened in ~p~n", [a_module]).</input>
-
-=INFO REPORT==== 11-Aug-2005::14:06:15 ===
+1> <input>error_logger:info_msg("Something happened in ~p", [a_module]).</input>
+=INFO REPORT==== 22-May-2018::12:03:32.612462 ===
 Something happened in a_module
 ok</pre>
         <warning>
-          <p>If called with bad arguments, this function can crash
-            the standard event handler, meaning no further events are
-            logged. When in doubt, use <c>info_report/1</c> instead.</p>
-        </warning>
-        <warning>
           <p>If the Unicode translation modifier (<c>t</c>) is used in
-            the format string, all error handlers must ensure that the
+            the format string, all event handlers must ensure that the
             formatted output is correctly encoded for the I/O
             device.</p>
         </warning>
@@ -230,37 +245,52 @@ ok</pre>
     </func>
     <func>
       <name name="info_report" arity="1"/>
-      <fsummary>Send a standard information report event to the error logger.</fsummary>
+      <fsummary>Log a standard information event.</fsummary>
       <desc>
-        <p>Sends a standard information report event to the error
-          logger. The event is handled by the standard event handler.</p>
+        <p>Log a standard information event. Error logger forwards the
+          event to Logger, including metadata that allows backwards
+          compatibility with legacy error logger event handlers.</p>
+	<p>The event is handled by the default Logger handler.</p>
+	<p>This functions is kept for backwards compatibility and
+	  must not be used by new code. Use the <seealso marker="logger#macros">
+	    <c>?LOG_INFO</c></seealso> macro or
+	  <seealso marker="logger#info-1"><c>logger:info/1,2,3</c></seealso>
+	  instead.</p>
 	<p><em>Example:</em></p>
         <pre>
 2> <input>error_logger:info_report([{tag1,data1},a_term,{tag2,data}]).</input>
-
-=INFO REPORT==== 11-Aug-2005::13:55:09 ===
+=INFO REPORT==== 22-May-2018::12:06:35.994440 ===
     tag1: data1
     a_term
     tag2: data
 ok
 3> <input>error_logger:info_report("Something strange happened").</input>
-
-=INFO REPORT==== 11-Aug-2005::13:55:36 ===
+=INFO REPORT==== 22-May-2018::12:06:49.066872 ===
 Something strange happened
 ok</pre>
       </desc>
     </func>
     <func>
       <name name="info_report" arity="2"/>
-      <fsummary>Send a user-defined information report event to the error logger.</fsummary>
+      <fsummary>Log a user-defined information event.</fsummary>
       <desc>
-        <p>Sends a user-defined information report event to the error
-          logger. An event handler to handle the event is supposed to
-          have been added. The event is ignored by the standard event
-          handler.</p>
+        <p>Log a user-defined information event. Error logger forwards
+          the event to Logger, including metadata that allows
+          backwards compatibility with legacy error logger event
+          handlers.</p>
+	<p>Error logger also adds a <c>domain</c> field with
+          value <c>[<anno>Type</anno>]</c> to this event's metadata,
+          causing the filters of the default Logger handler to discard
+          the event. A different Logger handler, or an error logger
+          event handler, must be added to handle this event.</p>
         <p>It is recommended that <c><anno>Report</anno></c> follows the same
           structure as for
 	<seealso marker="#info_report/1"><c>info_report/1</c></seealso>.</p>
+	<p>This functions is kept for backwards compatibility and
+	  must not be used by new code. Use the <seealso marker="logger#macros">
+	    <c>?LOG_INFO</c></seealso> macro or
+	  <seealso marker="logger#info-1"><c>logger:info/1,2,3</c></seealso>
+	  instead.</p>
       </desc>
     </func>
     <func>
@@ -359,24 +389,27 @@ ok</pre>
     <func>
       <name name="warning_msg" arity="1"/>
       <name name="warning_msg" arity="2"/>
-      <fsummary>Send a standard warning event to the error logger.</fsummary>
+      <fsummary>Log a standard warning event.</fsummary>
       <desc>
-        <p>Sends a standard warning event to the error logger.
-          The <c><anno>Format</anno></c> and <c><anno>Data</anno></c> arguments
-	  are the same as the arguments of
+        <p>Log a standard warning event. The <c><anno>Format</anno></c>
+          and <c><anno>Data</anno></c> arguments are the same as the
+          arguments of
 	  <seealso marker="stdlib:io#format/2"><c>io:format/2</c></seealso>
-	  in STDLIB.
-	  The event is handled by the standard event handler. It is tagged
-	  as an error, warning, or info, see
+	  in STDLIB.</p>
+        <p>Error logger forwards the event to Logger, including
+          metadata that allows backwards compatibility with legacy
+          error logger event handlers.</p>
+	<p>The event is handled by the default Logger handler. The log
+	  level can be changed to error or info, see
           <seealso marker="#warning_map/0"><c>warning_map/0</c></seealso>.</p>
-        <warning>
-          <p>If called with bad arguments, this function can crash
-            the standard event handler, meaning no further events are
-            logged. When in doubt, use <c>warning_report/1</c> instead.</p>
-        </warning>
+	<p>These functions are kept for backwards compatibility and
+	  must not be used by new code. Use the <seealso marker="logger#macros">
+	    <c>?LOG_WARNING</c></seealso> macro or
+	  <seealso marker="logger#warning-1"><c>logger:warning/1,2,3</c></seealso>
+	  instead.</p>
         <warning>
           <p>If the Unicode translation modifier (<c>t</c>) is used in
-            the format string, all error handlers must ensure that the
+            the format string, all event handlers must ensure that the
             formatted output is correctly encoded for the I/O
             device.</p>
         </warning>
@@ -384,24 +417,43 @@ ok</pre>
     </func>
     <func>
       <name name="warning_report" arity="1"/>
-      <fsummary>Send a standard warning report event to the error logger.</fsummary>
+      <fsummary>Log a standard warning event.</fsummary>
       <desc>
-        <p>Sends a standard warning report event to the error logger.
-          The event is handled by the standard event handler. It is
-          tagged as an error, warning, or info, see
+        <p>Log a standard warning event. Error logger forwards the event
+          to Logger, including metadata that allows backwards
+          compatibility with legacy error logger event handlers.</p>
+	<p>The event is handled by the default Logger handler. The log
+	  level can be changed to error or info, see
           <seealso marker="#warning_map/0"><c>warning_map/0</c></seealso>.</p>
+	<p>This functions is kept for backwards compatibility and
+	  must not be used by new code. Use the <seealso marker="logger#macros">
+	    <c>?LOG_WARNING</c></seealso> macro or
+	  <seealso marker="logger#warning-1"><c>logger:warning/1,2,3</c></seealso>
+	  instead.</p>
       </desc>
     </func>
     <func>
       <name name="warning_report" arity="2"/>
-      <fsummary>Send a user-defined warning report event to the error logger.</fsummary>
+      <fsummary>Log a user-defined warning event.</fsummary>
       <desc>
-        <p>Sends a user-defined warning report event to the error
-          logger. An event handler to handle the event is supposed to
-          have been added. The event is ignored by the standard event
-          handler. It is tagged as an error, warning, or info,
-          depending on the value of
+        <p>Log a user-defined warning event. Error logger forwards the
+          event to Logger, including metadata that allows backwards
+          compatibility with legacy error logger event handlers.</p>
+	<p>Error logger also adds a <c>domain</c> field with
+          value <c>[<anno>Type</anno>]</c> to this event's metadata,
+          causing the filters of the default Logger handler to discard
+          the event. A different Logger handler, or an error logger
+          event handler, must be added to handle this event.</p>
+	<p>The log level can be changed to error or info, see
           <seealso marker="#warning_map/0"><c>warning_map/0</c></seealso>.</p>
+        <p>It is recommended that <c><anno>Report</anno></c> follows the same
+          structure as for
+	<seealso marker="#warning_report/1"><c>warning_report/1</c></seealso>.</p>
+	<p>This functions is kept for backwards compatibility and
+	  must not be used by new code. Use the <seealso marker="logger#macros">
+	    <c>?LOG_WARNING</c></seealso> macro or
+	  <seealso marker="logger#warning-1"><c>logger:warning/1,2,3</c></seealso>
+	  instead.</p>
       </desc>
     </func>
   </funcs>
@@ -465,8 +517,9 @@ ok</pre>
   <section>
     <title>See Also</title>
     <p><seealso marker="stdlib:gen_event"><c>gen_event(3)</c></seealso>,
-       <seealso marker="stdlib:log_mf_h"><c>log_mf_h(3)</c></seealso>
-       <seealso marker="kernel_app"><c>kernel(6)</c></seealso>
+       <seealso marker="kernel:logger"><c>logger(3)</c></seealso>,
+       <seealso marker="stdlib:log_mf_h"><c>log_mf_h(3)</c></seealso>,
+       <seealso marker="kernel_app"><c>kernel(6)</c></seealso>,
        <seealso marker="sasl:sasl_app"><c>sasl(6)</c></seealso></p>
   </section>
 </erlref>
diff --git a/lib/kernel/doc/src/introduction_chapter.xml b/lib/kernel/doc/src/introduction_chapter.xml
index 6e6990ddda..2eadc70abf 100644
--- a/lib/kernel/doc/src/introduction_chapter.xml
+++ b/lib/kernel/doc/src/introduction_chapter.xml
@@ -46,7 +46,6 @@
       <item>Start, stop, supervision, configuration, and distribution of applications</item>
       <item>Code loading</item>
       <item>Logging</item>
-      <item>Error logging</item>
       <item>Global name service</item>
       <item>Supervision of Erlang/OTP</item>
       <item>Communication with sockets</item>
diff --git a/lib/kernel/doc/src/kernel_app.xml b/lib/kernel/doc/src/kernel_app.xml
index 7cd05dab14..e2a6d30249 100644
--- a/lib/kernel/doc/src/kernel_app.xml
+++ b/lib/kernel/doc/src/kernel_app.xml
@@ -42,7 +42,6 @@
       <item>Start, stop, supervision, configuration, and distribution of applications</item>
       <item>Code loading</item>
       <item>Logging</item>
-      <item>Error logging</item>
       <item>Global name service</item>
       <item>Supervision of Erlang/OTP</item>
       <item>Communication with sockets</item>
@@ -193,10 +192,10 @@
 	  will not log any progress-, crash-, or supervisor reports.
           If the SASL application is started,
 	  these log events will be sent to a second handler instance
-	  named <c>sasl_h</c>, according to values of the SASL
-	  environment variables <c>sasl_error_logger</c>
+	  named <c>sasl</c>, according to values of the SASL
+	  configuration parameter <c>sasl_error_logger</c>
 	  and <c>sasl_errlog_type</c>, see
-	  <seealso marker="sasl:sasl_app#configuration">SASL(6)
+	  <seealso marker="sasl:sasl_app#deprecated_error_logger_config">sasl(6)
 	</seealso></p>
 	<p>The default value is <c>false</c>.</p>
 	<p>See chapter <seealso marker="logger_chapter#compatibility">Backwards
@@ -205,17 +204,17 @@
         <note><p>This configuration option only effects the <c>default</c>
           and <c>sasl</c> handler. Any other handlers are uneffected.</p></note>
       </item>
-      <tag><marker id="logger_log_progress"/>
-	<c>logger_log_progress = boolean()</c></tag>
+      <tag><marker id="logger_progress_reports"/>
+	<c>logger_progress_reports = stop | log</c></tag>
       <item>
 	<p>If <c>logger_sasl_compatible = false</c>,
-	  then <c>logger_log_progress</c> specifies if progress
+	  then <c>logger_progress_reports</c> specifies if progress
 	  reports from <c>supervisor</c>
 	  and <c>application_controller</c> shall be logged by the
           default logger.</p>
 	<p>If <c>logger_sasl_compatible = true</c>,
-	  then <c>logger_log_progress</c> is ignored.</p>
-        <p>The default value is <c>false</c></p>
+	  then <c>logger_progress_reports</c> is ignored.</p>
+        <p>The default value is <c>stop</c></p>
         <note><p>This configuration option only effects the <c>default</c>
           and <c>sasl</c> handler. Any other handlers are uneffected.</p></note>
       </item>
@@ -271,7 +270,7 @@
       <tag><c>inet_parse_error_log = silent</c></tag>
       <item>
         <p>If set, no
-          <c>error_logger</c> messages are generated when erroneous
+          <c>logger</c> messages are generated when erroneous
           lines are found and skipped in the various Inet configuration
           files.</p>
       </item>
@@ -482,13 +481,13 @@ MaxT = TickTime + TickTime / 4</code>
 
   <section>
     <title>Deprecated Configuration Parameters</title>
-    <p>In OTP-21, a new API for logging was added to Erlang/OTP. The
+    <p>In Erlang/OTP 21.0, a new API for logging was added. The
       old <c>error_logger</c> event manager, and event handlers
-      running on this manager, will still work, but they are not used
+      running on this manager, still work, but they are no longer used
       by default.</p>
-    <p>The following application environment variables can still be
-      set, but they will only be used if the corresponding new logger
-      variables are not set.</p>
+    <p>The following application configuration parameters can still be
+      set, but they are only used if the corresponding configuration
+      parameters for Logger are not set.</p>
     <taglist>
       <tag><c>error_logger</c></tag>
       <item>Replaced by setting the type of the default
@@ -519,12 +518,12 @@ erl -kernel logger '[{handler,default,logger_std_h,#{formatter=>{logger_formatte
       <seealso marker="disk_log"><c>disk_log(3)</c></seealso>,
       <seealso marker="erl_boot_server"><c>erl_boot_server(3)</c></seealso>,
       <seealso marker="erl_ddll"><c>erl_ddll(3)</c></seealso>,
-      <seealso marker="error_logger"><c>error_logger(3)</c></seealso>,
       <seealso marker="file"><c>file(3)</c></seealso>,
       <seealso marker="global"><c>global(3)</c></seealso>,
       <seealso marker="global_group"><c>global_group(3)</c></seealso>,
       <seealso marker="heart"><c>heart(3)</c></seealso>,
       <seealso marker="inet"><c>inet(3)</c></seealso>,
+      <seealso marker="logger"><c>logger(3)</c></seealso>,
       <seealso marker="net_kernel"><c>net_kernel(3)</c></seealso>,
       <seealso marker="os"><c>os(3)</c></seealso>,
       <seealso marker="pg2"><c>pg2(3)</c></seealso>,
diff --git a/lib/kernel/doc/src/logger.xml b/lib/kernel/doc/src/logger.xml
index 2ee1059df8..911eb158da 100644
--- a/lib/kernel/doc/src/logger.xml
+++ b/lib/kernel/doc/src/logger.xml
@@ -33,23 +33,24 @@
     <file>logger.xml</file>
   </header>
   <module>logger</module>
-  <modulesummary>API module for the logger.</modulesummary>
+  <modulesummary>API module for logging in Erlang/OTP.</modulesummary>
 
   <description>
     <p>
-      This module is the main logger API. It contains functions that allow
-      application to use a single log API and the system to manage those log
-      events independently. To log events the logger
-      <seealso marker="#macros">macros</seealso> should be used. For instance,
-      to log a new error log event:</p>
+      This module is the main API for logging in Erlang/OTP. It
+      contains functions that allow applications to use a single log
+      API and the system to manage those log events independently. Use
+      the <seealso marker="#emergency-1">API functions</seealso> or the log
+      <seealso marker="#macros">macros</seealso> to log events. For instance,
+      to log a new error event:</p>
       <code>
 ?LOG_ERROR("error happened because: ~p",[Reason]). %% With macro
 logger:error("error happened because: ~p",[Reason]). %% Without macro
       </code>
-      <p>This log event will then be sent to the configured log handlers which
-      by default means that it will be printed to the console. If you want
+      <p>This log event is then sent to the configured log handlers which
+      by default means that it is be printed to the console. If you want
       your systems logs to be printed to a file instead of the console you
-      have to configure the default handler to do so. The simplest way is
+      must configure the default handler to do so. The simplest way is
       to include the following in your <seealso marker="config"><c>sys.config</c></seealso>.</p>
       <code>
 [{kernel,
@@ -63,7 +64,7 @@ logger:error("error happened because: ~p",[Reason]). %% Without macro
     <list type="bulleted">
       <item>how to use the API,
         see <seealso marker="logger_chapter">the User's Guide</seealso>.</item>
-      <item>how to configure logger,
+      <item>how to configure Logger,
         see the <seealso marker="logger_chapter#configuration">Configuration</seealso>
         section in the User's Guide.</item>
       <item>the convinience macros in logger.hrl,
@@ -86,7 +87,7 @@ logger:error("error happened because: ~p",[Reason]). %% Without macro
       </desc>
     </datatype>
     <datatype>
-      <name name="log"/>
+      <name name="log_event"/>
       <desc>
 	<p></p>
       </desc>
@@ -111,7 +112,7 @@ logger:error("error happened because: ~p",[Reason]). %% Without macro
 	<list>
 	  <item><c>pid  => self()</c></item>
 	  <item><c>gl   => group_leader()</c></item>
-	  <item><c>time => erlang:monotonic_time(microsecond)</c></item>
+	  <item><c>time => erlang:system_time(microsecond)</c></item>
 	</list>
 	<p>When a log macro is used, Logger also inserts location
 	  information:</p>
@@ -129,8 +130,31 @@ logger:error("error happened because: ~p",[Reason]). %% Without macro
 	    <c>update_process_metadata/1</c></seealso>.</p>
 	<p>Logger merges all the metadata maps before forwarding the
 	  log event to the handlers. If the same keys occur, values
-	  from the log call overwrites process metadata, which in turn
-	  overwrites values set by Logger.</p>
+	  from the log call overwrite process metadata, which in turn
+	  overwrite values set by Logger.</p>
+	<p>The following custom metadata keys have special meaning:</p>
+	<taglist>
+	  <tag><c>domain</c></tag>
+	  <item>
+	    <p>The value associated with this key is used by filters
+	      for grouping log events originating from, for example,
+	      specific functional
+	      areas. See <seealso marker="logger_filters#domain-2">
+		<c>logger_filters:domain/2</c></seealso>
+	      for a description of how this field can be used.</p>
+	  </item>
+	  <tag><c>report_cb</c></tag>
+	  <item>
+	    <p>If the log message is specified as
+	      a <seealso marker="#type-report"><c>report()</c></seealso>,
+	      the <c>report_cb</c> key can be associated with a fun
+	      (report callback) that converts the report to a format
+	      string and arguments. See
+	      section <seealso marker="logger_chapter#log_message">Log
+	      Message</seealso> in the User's Guide for more
+	      information about report callbacks.</p>
+	  </item>
+	</taglist>
       </desc>
     </datatype>
     <datatype>
@@ -144,7 +168,7 @@ logger:error("error happened because: ~p",[Reason]). %% Without macro
 	  <item><c>filters => []</c></item>
 	  <item><c>formatter => {logger_formatter,DefaultFormatterConfig</c>}</item>
 	</list>
-	<p>See the <seealso marker="logger_formatter#configuration">
+	<p>See the <seealso marker="logger_formatter#type-config">
 	    <c>logger_formatter(3)</c></seealso> manual page for
 	  information about the default configuration for this
 	  formatter.</p>
@@ -165,7 +189,8 @@ logger:error("error happened because: ~p",[Reason]). %% Without macro
     <datatype>
       <name name="filter"/>
       <desc>
-	<p>A filter which can be installed for logger or for a handler.</p>
+	<p>A filter which can be installed for the logger part of
+	  Logger, or for a handler.</p>
       </desc>
     </datatype>
     <datatype>
@@ -184,8 +209,17 @@ logger:error("error happened because: ~p",[Reason]). %% Without macro
       <name name="timestamp"/>
       <desc>
 	<p>A timestamp produced
-	  with <seealso marker="erts:erlang#monotonic_time-1">
-	    <c>erlang:monotonic_time(microsecond)</c></seealso>.</p>
+	  with <seealso marker="erts:erlang#system_time-1">
+	    <c>erlang:system_time(microsecond)</c></seealso>.</p>
+      </desc>
+    </datatype>
+    <datatype>
+      <name name="formatter_config"/>
+      <desc>
+	<p>Configuration data for the
+	formatter. See <seealso marker="logger_formatter">
+	    <c>logger_formatter(3)</c></seealso>
+	  for an example of a formatter implementation.</p>
       </desc>
     </datatype>
   </datatypes>
@@ -213,9 +247,9 @@ logger:error("error happened because: ~p",[Reason]). %% Without macro
       <item><c>?LOG_DEBUG(FunOrFormat,Args[,Metadata])</c></item>
     </list>
 
-    <p>All macros expand to a call to logger, where <c>Level</c> is
-      taken from the macro name, and location data is added. See the
-      description of
+    <p>All macros expand to a call to Logger, where <c>Level</c> is
+      taken from the macro name, and location data is added to the
+      metadata. See the description of
       the <seealso marker="#type-metadata"><c>metadata()</c></seealso>
       type for more information about the location data.</p>
 
@@ -335,23 +369,26 @@ logger:error("error happened because: ~p",[Reason]). %% Without macro
 
     <func>
       <name name="get_logger_config" arity="0"/>
-      <fsummary>Lookup the current configuration for logger.</fsummary>
+      <fsummary>Look up the current configuration for the logger part
+	of Logger.</fsummary>
       <desc>
-        <p>Lookup the current configuration for logger.</p>
+        <p>Look up the current configuration for the logger part of
+          Logger.</p>
       </desc>
     </func>
 
     <func>
       <name name="get_handler_config" arity="1"/>
-      <fsummary>Lookup the current configuration for the given handler.</fsummary>
+      <fsummary>Look up the current configuration for the given
+	handler.</fsummary>
       <desc>
-        <p>Lookup the current configuration for the given handler.</p>
+        <p>Look up the current configuration for the given handler.</p>
       </desc>
     </func>
 
     <func>
       <name name="i" arity="0"/>
-      <fsummary>Get all logger configurations</fsummary>
+      <fsummary>Get all Logger configurations</fsummary>
       <desc>
         <p>Same as <seealso marker="#i/1"><c>logger:i(term)</c></seealso></p>
       </desc>
@@ -361,28 +398,28 @@ logger:error("error happened because: ~p",[Reason]). %% Without macro
       <name name="i" arity="1" clause_i="1"/>
       <name name="i" arity="1" clause_i="2"/>
       <name name="i" arity="1" clause_i="3"/>
-      <fsummary>Get all logger configurations</fsummary>
+      <fsummary>Get all Logger configurations</fsummary>
       <desc>
-        <p>Display or return all current logger configuration.</p>
+        <p>Display or return all current Logger configurations.</p>
         <taglist>
           <tag><c><anno>Action</anno> = string</c></tag>
           <item>
-	    <p>Return the pretty printed current logger configuration
+	    <p>Return the pretty printed current Logger configuration
               as iodata.</p>
 	  </item>
           <tag><c><anno>Action</anno> = term</c></tag>
           <item>
-	    <p>Return the current logger configuration as a term. The
-              format of this term may change inbetween releases. For a
+	    <p>Return the current Logger configuration as a term. The
+              format of this term may change between releases. For a
               stable format use <seealso marker="#get_handler_config/1">
 	      <c>logger:get_handler_config/1</c></seealso>
               and <seealso marker="#get_logger_config/0">
-	      <c>logger:get_logger_config/0</c></seealso>.
-              The same as calling <c>logger:i()</c>.</p>
+	      <c>logger:get_logger_config/0</c></seealso>.</p>
+            <p>The same as calling <c>logger:i()</c>.</p>
 	  </item>
 	  <tag><c><anno>Action</anno> = print</c></tag>
           <item>
-	    <p>Pretty print all the current logger configuration to
+	    <p>Pretty print all the current Logger configuration to
               standard out. Example:</p>
             <code><![CDATA[1> logger:i(print).
 Current logger configuration:
@@ -407,10 +444,10 @@ Current logger configuration:
           Config: stop
         Id: domain
           Fun:    fun logger_filters:domain/2
-          Config: {log,prefix_of,[beam,erlang,otp,sasl]}
+          Config: {log,super,[beam,erlang,otp,sasl]}
         Id: no_domain
           Fun:    fun logger_filters:domain/2
-          Config: {log,no_domain,[]}
+          Config: {log,undefined,[]}
       Handler Config:
         logger_std_h: #{type => standard_io}
   Level set per module:
@@ -423,21 +460,21 @@ Current logger configuration:
 
     <func>
       <name name="add_logger_filter" arity="2"/>
-      <fsummary>Add a filter to the logger.</fsummary>
+      <fsummary>Add a filter to the logger part of Logger.</fsummary>
       <desc>
-        <p>Add a filter to the logger.</p>
+        <p>Add a filter to the logger part of Logger.</p>
 	<p>The filter fun is called with the log event as the first
 	  parameter, and the specified <c>filter_args()</c> as the
 	  second parameter.</p>
 	<p>The return value of the fun specifies if a log event is to
 	  be discarded or forwarded to the handlers:</p>
 	<taglist>
-	  <tag><c>log()</c></tag>
+	  <tag><c>log_event()</c></tag>
 	  <item>
 	    <p>The filter <em>passed</em>. The next logger filter, if
 	      any, is applied. If no more logger filters exist, the
-	      log event is forwarded to the handler part of the
-	      logger, where handler filters are applied.</p>
+	      log event is forwarded to the handler part of Logger,
+	      where handler filters are applied.</p>
 	  </item>
 	  <tag><c>stop</c></tag>
 	  <item>
@@ -449,13 +486,13 @@ Current logger configuration:
 	    <p>The filter has no knowledge of the log event. The next
 	      logger filter, if any, is applied. If no more logger
 	      filters exist, the value of the <c>filter_default</c>
-	      configuration parameter for the logger specifies if the
-	      log event shall be discarded or forwarded to the handler
-	      part.</p>
+	      configuration parameter for the logger part specifies if
+	      the log event shall be discarded or forwarded to the
+	      handler part.</p>
 	  </item>
 	</taglist>
-	<p>See section <seealso marker="logger_chapter#Filter">
-	    Filter</seealso> in the User's Guide for more information
+	<p>See section <seealso marker="logger_chapter#filters">
+	    Filters</seealso> in the User's Guide for more information
 	    about filters.</p>
 	<p>Some built-in filters exist. These are defined
 	  in <seealso marker="logger_filters"><c>logger_filters</c></seealso>.</p>
@@ -473,7 +510,7 @@ Current logger configuration:
 	<p>The return value of the fun specifies if a log event is to
 	  be discarded or forwarded to the handler callback:</p>
 	<taglist>
-	  <tag><c>log()</c></tag>
+	  <tag><c>log_event()</c></tag>
 	  <item>
 	    <p>The filter <em>passed</em>. The next handler filter, if
 	      any, is applied. If no more filters exist for this
@@ -496,7 +533,7 @@ Current logger configuration:
 	  </item>
 	</taglist>
 	<p>See
-	  section <seealso marker="logger_chapter#Filter">Filter</seealso>
+	  section <seealso marker="logger_chapter#filters">Filters</seealso>
 	  in the User's Guide for more information about filters.</p>
 	<p>Some built-in filters exist. These are defined in
 	  <seealso marker="logger_filters"><c>logger_filters</c></seealso>.</p>
@@ -505,10 +542,10 @@ Current logger configuration:
 
     <func>
       <name name="remove_logger_filter" arity="1"/>
-      <fsummary>Remove a filter from the logger.</fsummary>
+      <fsummary>Remove a filter from the logger part of Logger.</fsummary>
       <desc>
         <p>Remove the filter identified
-          by <c><anno>FilterId</anno></c> from the logger.</p>
+          by <c><anno>FilterId</anno></c> from the logger part of Logger.</p>
       </desc>
     </func>
 
@@ -548,21 +585,21 @@ Current logger configuration:
         <p>Set the log level for the
           specified <c><anno>Module</anno></c>.</p>
 	<p>The log level for a module overrides the global log level
-	  of the logger for log event originating from the module in
+	  of Logger for log events originating from the module in
 	  question. Notice, however, that it does not override the
 	  level configuration for any handler.</p>
-	<p>For example: Assume that the global log level for the
-	  logger is <c>info</c>, and there is one handler, <c>h1</c>,
-	  with level <c>info</c> and one handler, <c>h2</c>, with
+	<p>For example: Assume that the global log level for Logger
+	  is <c>info</c>, and there is one handler, <c>h1</c>, with
+	  level <c>info</c> and one handler, <c>h2</c>, with
 	  level <c>debug</c>.</p>
 	<p>With this configuration, no debug messages will be logged,
 	  since they are all stopped by the global log level.</p>
-	<p>If the level for <c>mymodule</c> is set now set
+	<p>If the level for <c>mymodule</c> is now set
 	  to <c>debug</c>, then debug events from this module will be
 	  logged by the handler <c>h2</c>, but not by
 	  handler <c>h1</c>.</p>
 	<p>Debug events from other modules are still not logged.</p>
-        <p>To change the global log level for the logger, use
+        <p>To change the global log level for Logger, use
           <seealso marker="#set_logger_config/2">
 	    <c>logger:set_logger_config(level,Level)</c></seealso>.</p>
         <p>To change the log level for a handler, use
@@ -572,15 +609,16 @@ Current logger configuration:
 	  <p>The originating module for a log event is only detected
 	    if <c>mfa=>{Module,Function,Arity}</c> exists in the
 	    metadata. When log macros are used, this association is
-	    automatically added to all log events. If the logger API
+	    automatically added to all log events. If an API function
 	    is called directly, without using a macro, the logging
-	    client must explicitly add this information.</p>
+	    client must explicitly add this information if module
+	    levels shall have any effect.</p>
 	</note>
       </desc>
     </func>
 
     <func>
-      <name name="reset_module_level" arity="1"/>
+      <name name="unset_module_level" arity="1"/>
       <fsummary>Remove a module specific log setting.</fsummary>
       <desc>
         <p>Remove a module specific log setting. After this, the
@@ -590,10 +628,11 @@ Current logger configuration:
 
     <func>
       <name name="add_handlers" arity="1" clause_i="1"/>
-      <fsummary>Setup logger handlers from the applications configuration parameters.</fsummary>
+      <fsummary>Set up log handlers from the application's
+	configuration parameters.</fsummary>
       <desc>
         <p>Reads the application configuration parameter <c>logger</c> and
-          calls <c>logger:add_handlers/1</c> with it contents.</p>
+          calls <c>logger:add_handlers/1</c> with its contents.</p>
       </desc>
     </func>
 
@@ -602,11 +641,12 @@ Current logger configuration:
       <fsummary>Setup logger handlers.</fsummary>
       <type name="config_handler"/>
       <desc>
-        <p>This function should be used by custom logger handlers to make
+        <p>This function should be used by custom Logger handlers to make
         configuration consistent no matter which handler the system uses.
-        Normal usage to to add a call to <c>logger:add_handlers/1</c>
-        just after the processes that the handler needs are started
-        and pass the applications logger config as an argument. Eg.</p>
+        Normal usage is to add a call to <c>logger:add_handlers/1</c>
+        just after the processes that the handler needs are started,
+        and pass the application's <c>logger</c> configuration as the argument.
+	For example:</p>
         <code>
 -behaviour(application).
 start(_, []) ->
@@ -616,19 +656,20 @@ start(_, []) ->
             {ok, Pid, []};
         Error -> Error
      end.</code>
-       <p>This will read the <c>logger</c> configuration parameter from
-         the handler application and start the configured handlers. The contents
-         of the configuration use the same rules as the
+       <p>This reads the <c>logger</c> configuration parameter from
+         the <c>my_all</c> application and starts the configured
+         handlers. The contents of the configuration use the same
+         rules as the
          <seealso marker="logger_chapter#handler-configuration">logger handler configuration</seealso>.
        </p>
-       <p>If the handler is meant to replace the default handler the kernels
-         default handlers have to be disabled before the new handler is added.
-         A <c>sys.config</c> file that disables the kernel handler and adds
-         a custom handler could looks like this:</p>
+       <p>If the handler is meant to replace the default handler, the Kernel's
+         default handler have to be disabled before the new handler is added.
+         A <c>sys.config</c> file that disables the Kernel handler and adds
+         a custom handler could look like this:</p>
          <code>
 [{kernel,
   [{logger,
-    %% Disable the default kernel handler
+    %% Disable the default Kernel handler
     [{handler,default,undefined}]}]},
  {my_app,
   [{logger,
@@ -640,10 +681,10 @@ start(_, []) ->
 
     <func>
       <name name="set_logger_config" arity="1"/>
-      <fsummary>Set configuration data for the logger.</fsummary>
+      <fsummary>Set configuration data for the logger part of Logger.</fsummary>
       <desc>
-        <p>Set configuration data for the logger. This overwrites the
-          current logger configuration.</p>
+        <p>Set configuration data for the logger part of Logger. This
+          overwrites the current logger configuration.</p>
 	<p>To modify the existing configuration,
 	  use <seealso marker="#update_logger_config-1">
 	    <c>update_logger_config/1</c></seealso>, or, if a more
@@ -658,21 +699,25 @@ start(_, []) ->
 
     <func>
       <name name="set_logger_config" arity="2"/>
-      <fsummary>Add or update configuration data for the logger.</fsummary>
+      <fsummary>Add or update configuration data for the logger part
+	of Logger.</fsummary>
       <desc>
-        <p>Add or update configuration data for the logger. If the
-          given <c><anno>Key</anno></c> already exists, its associated
-          value will be changed to <c><anno>Value</anno></c>. If it
-          does not exist, it will be added.</p>
+        <p>Add or update configuration data for the logger part of
+          Logger. If the given <c><anno>Key</anno></c> already exists,
+          its associated value will be changed
+          to <c><anno>Value</anno></c>. If it does not exist, it will
+          be added.</p>
       </desc>
     </func>
 
     <func>
       <name name="update_logger_config" arity="1"/>
-      <fsummary>Update configuration data for the logger.</fsummary>
+      <fsummary>Update configuration data for the logger part of
+	Logger.</fsummary>
       <desc>
-        <p>Update configuration data for the logger. This function
-          behaves as if it was implemented as follows:</p>
+        <p>Update configuration data for the logger part of
+          Logger. This function behaves as if it was implemented as
+          follows:</p>
 	<code type="erl">
 {ok,Old} = logger:get_logger_config(),
 logger:set_logger_config(maps:merge(Old,Config)).
@@ -697,7 +742,7 @@ logger:set_logger_config(maps:merge(Old,Config)).
 	  </seealso>, then do the merge before writing the new
 	  configuration back with this function.</p>
 	<p>If a key is removed compared to the current configuration,
-	  and the key is know by Logger, the default value is used. If
+	  and the key is known by Logger, the default value is used. If
 	  it is a custom key, then it is up to the handler
 	  implementation if the value is removed or a default value is
 	  inserted.</p>
@@ -734,6 +779,31 @@ logger:set_handler_config(HandlerId,maps:merge(Old,Config)).
     </func>
 
     <func>
+      <name name="update_formatter_config" arity="2"/>
+      <fsummary>Update the formatter configuration for the specified handler.</fsummary>
+      <desc>
+        <p>Update the formatter configuration for the specified handler.</p>
+	<p>The new configuration is merged with the existing formatter
+	  configuration.</p>
+	<p>To overwrite the existing configuration without any merge,
+	  use <seealso marker="#set_handler_config-3">
+	    <c>set_handler_config(HandlerId,formatter,
+	      {FormatterModule,FormatterConfig})</c></seealso>.</p>
+      </desc>
+    </func>
+
+    <func>
+      <name name="update_formatter_config" arity="3"/>
+      <fsummary>Update the formatter configuration for the specified handler.</fsummary>
+      <desc>
+        <p>Update the formatter configuration for the specified handler.</p>
+	<p>This is equivalent
+	  to <br/><seealso marker="#update_formatter_config-2">
+	    <c>update_formatter_config(<anno>HandlerId</anno>,#{<anno>Key</anno>=><anno>Value</anno>})</c></seealso></p>
+      </desc>
+    </func>
+
+    <func>
       <name name="compare_levels" arity="2"/>
       <fsummary>Compare the severity of two log levels.</fsummary>
       <desc>
@@ -826,18 +896,17 @@ logger:set_process_metadata(maps:merge(logger:get_process_metadata(),Meta)).
   </funcs>
 
   <section>
-    <title>Callback Functions</title>
+    <marker id="handler_callback_functions"/>
+    <title>Handler Callback Functions</title>
     <p>The following functions are to be exported from a handler
       callback module.</p>
   </section>
 
   <funcs>
     <func>
-      <name>Module:adding_handler(HandlerId,Config1) -> {ok,Config2} | {error,Reason}</name>
+      <name>HModule:adding_handler(Config1) -> {ok,Config2} | {error,Reason}</name>
       <fsummary>An instance of this handler is about to be added.</fsummary>
       <type>
-	<v>HandlerId =
-	  <seealso marker="#type-handler_id">handler_id()</seealso></v>
 	<v>Config1 = Config2 =
 	  <seealso marker="#type-config">config()</seealso></v>
 	<v>Reason = term()</v>
@@ -846,7 +915,9 @@ logger:set_process_metadata(maps:merge(logger:get_process_metadata(),Meta)).
 	<p>This callback function is optional.</p>
 	<p>The function is called when an new handler is about to be
 	  added, and the purpose is to verify the configuration and
-	  initiate all resourced needed by the handler.</p>
+	  initiate all resources needed by the handler.</p>
+	<p>The handler identity is associated with the <c>id</c> key
+	  in <c>Config1</c>.</p>
 	<p>If everything succeeds, the callback function can add
 	  possible default values or internal state values to the
 	  configuration, and return the adjusted map
@@ -857,28 +928,9 @@ logger:set_process_metadata(maps:merge(logger:get_process_metadata(),Meta)).
     </func>
 
     <func>
-      <name>Module:removing_handler(HandlerId,Config) -> ok</name>
-      <fsummary>The given handler is about to be removed.</fsummary>
-      <type>
-	<v>HandlerId =
-	  <seealso marker="#type-handler_id">handler_id()</seealso></v>
-	<v>Config =
-	  <seealso marker="#type-config">config()</seealso></v>
-      </type>
-      <desc>
-	<p>This callback function is optional.</p>
-	<p>The function is called when a handler is about to be
-	  removed, and the purpose is to release all resources used by
-	  the handler. The return value is ignored by Logger.</p>
-      </desc>
-    </func>
-
-    <func>
-      <name>Module:changing_config(HandlerId,Config1,Config2) -> {ok,Config3} | {error,Reason}</name>
+      <name>HModule:changing_config(Config1,Config2) -> {ok,Config3} | {error,Reason}</name>
       <fsummary>The configuration for this handler is about to change.</fsummary>
       <type>
-	<v>HandlerId =
-	  <seealso marker="#type-handler_id">handler_id()</seealso></v>
 	<v>Config1 = Config2 = Config3 =
 	  <seealso marker="#type-config">config()</seealso></v>
 	<v>Reason = term()</v>
@@ -890,12 +942,108 @@ logger:set_process_metadata(maps:merge(logger:get_process_metadata(),Meta)).
 	  the new configuration.</p>
 	<p><c>Config1</c> is the existing configuration
 	  and <c>Config2</c> is the new configuration.</p>
+	<p>The handler identity is associated with the <c>id</c> key
+	  in <c>Config1</c>.</p>
 	<p>If everything succeeds, the callback function must return a
 	  possibly adjusted configuration in <c>{ok,Config3}</c>.</p>
 	<p>If the configuration is faulty, the callback function must
 	  return <c>{error,Reason}</c>.</p>
       </desc>
     </func>
+
+    <func>
+      <name>HModule:log(LogEvent,Config) -> void()</name>
+      <fsummary>Log the given log event.</fsummary>
+      <type>
+	<v>LogEvent =
+	  <seealso marker="#type-log_event">log_event()</seealso></v>
+	<v>Config =
+	  <seealso marker="#type-config">config()</seealso></v>
+      </type>
+      <desc>
+	<p>This callback function is mandatory.</p>
+	<p>The function is called when all global filters and all
+	  handler filters for the handler in question have passed for
+	  the given log event.</p>
+	<p>The handler identity is associated with the <c>id</c> key
+	  in <c>Config</c>.</p>
+	<p>The handler must log the event.</p>
+	<p>The return value from this function is ignored by
+	  Logger.</p>
+      </desc>
+    </func>
+
+    <func>
+      <name>HModule:removing_handler(Config) -> ok</name>
+      <fsummary>The given handler is about to be removed.</fsummary>
+      <type>
+	<v>Config =
+	  <seealso marker="#type-config">config()</seealso></v>
+      </type>
+      <desc>
+	<p>This callback function is optional.</p>
+	<p>The function is called when a handler is about to be
+	  removed, and the purpose is to release all resources used by
+	  the handler.</p>
+	<p>The handler identity is associated with the <c>id</c> key
+	  in <c>Config</c>.</p>
+	<p>The return value is ignored by Logger.</p>
+      </desc>
+    </func>
+
+  </funcs>
+
+  <section>
+    <marker id="formatter_callback_functions"/>
+    <title>Formatter Callback Functions</title>
+    <p>The following functions are to be exported from a formatter
+      callback module.</p>
+  </section>
+
+  <funcs>
+    <func>
+      <name>FModule:check_config(FConfig) -> ok | {error,term()}</name>
+      <fsummary>Validate the given formatter configuration.</fsummary>
+      <type>
+	<v>FConfig =
+	  <seealso marker="#type-formatter_config">formatter_config()</seealso></v>
+      </type>
+      <desc>
+	<p>This callback function is optional.</p>
+	<p>The function is called by a Logger when formatter
+	  configuration is set or modified. The formatter must
+	  validate the given configuration and return <c>ok</c> if it
+	  is correct, and <c>{error,term()}</c> if it is faulty.</p>
+	<p>See <seealso marker="logger_formatter">
+	    <c>logger_formatter(3)</c></seealso>
+	  for an example implementation. <c>logger_formatter</c> is the
+	  default formatter used by Logger.</p>
+      </desc>
+    </func>
+    <func>
+      <name>FModule:format(LogEvent,FConfig) -> FormattedLogEntry</name>
+      <fsummary>Format the given log event.</fsummary>
+      <type>
+	<v>LogEvent =
+	  <seealso marker="#type-log_event">log_event()</seealso></v>
+	<v>FConfig =
+	  <seealso marker="#type-formatter_config">formatter_config()</seealso></v>
+	<v>FormattedLogEntry =
+	  <seealso marker="unicode#type-chardata">unicode:chardata()</seealso></v>
+      </type>
+      <desc>
+	<p>This callback function is mandatory.</p>
+	<p>The function can be called by a log handler to convert a
+	  log event term to a printable string. The returned value
+	  can, for example, be printed as a log entry to the console
+	  or a file using <seealso marker="stdlib:io#put_chars-1">
+	    <c>io:put_chars/1,2</c></seealso>.</p>
+	<p>See <seealso marker="logger_formatter">
+	    <c>logger_formatter(3)</c></seealso>
+	  for an example implementation. <c>logger_formatter</c> is the
+	  default formatter used by Logger.</p>
+      </desc>
+    </func>
   </funcs>
 </erlref>
 
diff --git a/lib/kernel/doc/src/logger_arch.png b/lib/kernel/doc/src/logger_arch.png
index 727609a6ef..901122193a 100644
--- a/lib/kernel/doc/src/logger_arch.png
+++ b/lib/kernel/doc/src/logger_arch.png
diff --git a/lib/kernel/doc/src/logger_chapter.xml b/lib/kernel/doc/src/logger_chapter.xml
index 4232429589..a3eec7bd4b 100644
--- a/lib/kernel/doc/src/logger_chapter.xml
+++ b/lib/kernel/doc/src/logger_chapter.xml
@@ -30,219 +30,403 @@
     <file>logger_chapter.xml</file>
   </header>
 
+  <p>Erlang/OTP 21.0 provides a new standard API for logging
+    through <c>Logger</c>, which is part of the Kernel
+    application. Logger consists of the API for issuing log events,
+    and a customizable backend where log handlers, filters and
+    formatters can be plugged in.</p>
+  <p>By default, the Kernel application installs one log handler at
+    system start. This handler is named <c>default</c>. It receives
+    and processes standard log events produced by the Erlang runtime
+    system, standard behaviours and different Erlang/OTP
+    applications. The log events are by default written to the
+    terminal.</p>
+  <p>You can also configure the system so that the default handler
+    prints log events to a single file, or to a set of wrap logs
+    via <seealso marker="disk_log"><c>disk_log</c></seealso>.</p>
+  <p>By confiugration, you can aslo modify or disable the default
+    handler, replace it by a custom handler, and install additional
+    handlers.</p>
+
   <section>
     <title>Overview</title>
-    <p>Erlang/OTP provides a standard API for logging. The backend of
-      this API can be used as is, or it can be customized to suite
-      specific needs.</p>
-    <p>It consists of two parts - the <em>logger</em> part and the
-      <em>handler</em> part. The logger will forward log events to one
-      or more handler(s).</p>
+    <p>A <em>log event</em> consists of a <em>log level</em>, the
+      <em>message</em> to be logged, and <em>metadata</em>.</p>
+    <p>The Logger backend forwards log events from the API, first
+      through a set of <em>global filters</em>, then through a set
+      of <em>handler filters</em> for each log handler.</p>
+    <p>Each filter set consists of a <em>log level check</em>,
+      followed by zero or more <em>filter functions</em>.</p>
+    <p>The following figure show a conseptual overview of Logger. The
+      figure shows two log handlers, but any number of handlers can be
+      installed.</p>
 
     <image file="logger_arch.png">
-      <icaption>Conceptual overview</icaption>
+      <icaption>Conceptual Overview</icaption>
     </image>
 
-    <p><em>Filters</em> can be added to the logger and to each
-      handler. The filters decide if an event is to be forwarded or
-      not, and they can also modify all parts of the log event.</p>
-
-    <p>A <em>formatter</em> can be set for each handler. The formatter
-      does the final formatting of the log event, including the log
-      message itself, and possibly a timestamp, header and other
-      metadata.</p>
-
-    <p>In accordance with the Syslog protocol, RFC-5424, eight
-      severity levels can be specified:</p>
-
-    <table align="left">
-      <row>
-	<cell><strong>Level</strong></cell>
-	<cell align="center"><strong>Integer</strong></cell>
-	<cell><strong>Description</strong></cell>
-      </row>
-      <row>
-	<cell>emergency</cell>
-	<cell align="center">0</cell>
-	<cell>system is unusable</cell>
-      </row>
-      <row>
-	<cell>alert</cell>
-	<cell align="center">1</cell>
-	<cell>action must be taken immediately</cell>
-      </row>
-      <row>
-	<cell>critical</cell>
-	<cell align="center">2</cell>
-	<cell>critical contidions</cell>
-      </row>
-      <row>
-	<cell>error</cell>
-	<cell align="center">3</cell>
-	<cell>error conditions</cell>
-      </row>
-      <row>
-	<cell>warning</cell>
-	<cell align="center">4</cell>
-	<cell>warning conditions</cell>
-      </row>
-      <row>
-	<cell>notice</cell>
-	<cell align="center">5</cell>
-	<cell>normal but significant conditions</cell>
-      </row>
-      <row>
-	<cell>info</cell>
-	<cell align="center">6</cell>
-	<cell>informational messages</cell>
-      </row>
-      <row>
-	<cell>debug</cell>
-	<cell align="center">7</cell>
-	<cell>debug-level messages</cell>
-      </row>
-      <tcaption>Severity levels</tcaption>
-    </table>
-
-    <p>A log event is allowed by Logger if the integer value of
-      its <c>Level</c> is less than or equal to the currently
-      configured log level. The log level can be configured globally,
-      or to allow more verbose logging from a specific part of the
-      system, per module.</p>
-
+    <p>Log levels are expressed as atoms. Internally in Logger, the
+      atoms are mapped to integer values, and a log event passes the
+      log level check if the integer value of its log level is less
+      than or equal to the currently configured log level. That is,
+      the check pases if the event is equally or more severe than the
+      configured level. See section <seealso marker="#log_level">Log
+      Level</seealso> for a listing and description of all log
+      levels.</p>
+    <p>The global log level can be overridden by a log level
+      configured per module. This is to, for instance, allow more
+      verbose logging from a specific part of the system.</p>
+    <p>Filter functions can be used for more sophisticated filtering
+      than the log level check provides. A filter function can stop or
+      pass a log event, based on any of the event's contents. It can
+      also modify all parts of the log event. See see
+      section <seealso marker="#filters">Filters</seealso> for more
+      details.</p>
+    <p>If a log event passes through all global filters and all
+      handler filters for a specific handler, Logger forwards the event
+      to the handler callback. The handler formats and prints the
+      event to its destination. See
+      section <seealso marker="#handlers">Handlers</seealso> for
+      more details.</p>
+    <p>Everything up to and including the call to the handler
+      callbacks is executed on the client process, that is, the
+      process where the log event was issued. It is up to the handler
+      implementation if other processes are involved or not.</p>
+    <p>The handlers are called in sequence, and the order is not
+      defined.</p>
+  </section>
+  <section>
+    <title>Logger API</title>
+    <p>The API for logging consists of a set
+      of <seealso marker="logger#macros">macros</seealso>, and a set
+      of functions on the form <c>logger:Level/1,2,3</c>, which are
+      all shortcuts
+      for <seealso marker="logger#log-2">
+	<c>logger:log(Level,Arg1[,Arg2[,Arg3]])</c></seealso>.</p>
+    <p>The difference between using the macros and the exported
+      functions is that macros add location (originator) information
+      to the metadata, and performs lazy evaluation by wrapping the
+      logger call in a case statement, so it is only evaluated if the
+      log level of the event passes the global log level check.</p>
     <section>
-      <title>Customizable parts</title>
-
+      <marker id="log_level"/>
+      <title>Log Level</title>
+      <p>The log level indicates the severity of a event. In
+	accordance with the Syslog protocol, RFC-5424, eight log
+	levels can be specified. The following table lists all
+	possible log levels by name (atom), integer value, and
+	description:</p>
+
+      <table align="left">
+	<row>
+	  <cell><strong>Level</strong></cell>
+	  <cell align="center"><strong>Integer</strong></cell>
+	  <cell><strong>Description</strong></cell>
+	</row>
+	<row>
+	  <cell>emergency</cell>
+	  <cell align="center">0</cell>
+	  <cell>system is unusable</cell>
+	</row>
+	<row>
+	  <cell>alert</cell>
+	  <cell align="center">1</cell>
+	  <cell>action must be taken immediately</cell>
+	</row>
+	<row>
+	  <cell>critical</cell>
+	  <cell align="center">2</cell>
+	  <cell>critical contidions</cell>
+	</row>
+	<row>
+	  <cell>error</cell>
+	  <cell align="center">3</cell>
+	  <cell>error conditions</cell>
+	</row>
+	<row>
+	  <cell>warning</cell>
+	  <cell align="center">4</cell>
+	  <cell>warning conditions</cell>
+	</row>
+	<row>
+	  <cell>notice</cell>
+	  <cell align="center">5</cell>
+	  <cell>normal but significant conditions</cell>
+	</row>
+	<row>
+	  <cell>info</cell>
+	  <cell align="center">6</cell>
+	  <cell>informational messages</cell>
+	</row>
+	<row>
+	  <cell>debug</cell>
+	  <cell align="center">7</cell>
+	  <cell>debug-level messages</cell>
+	</row>
+	<tcaption>Log Levels</tcaption>
+      </table>
+      <p>Notice that the integer value is only used internally in
+	Logger. In the API, you must always use the atom. To compare
+	the severity of two log levels,
+	use <seealso marker="logger#compare_levels-2">
+	  <c>logger:compare_levels/2</c></seealso>.</p>
+    </section>
+    <section>
+      <marker id="log_message"/>
+      <title>Log Message</title>
+      <p>The log message contains the information to be logged. The
+	message can consist of a format string and arguments (given as
+	two separate parameters in the Logger API), a string or a
+	report. The latter, which is either a map or a key-value list,
+	can be accompanied by a report callback specified in the log
+	event's <seealso marker="#metadata">metadata</seealso>. The
+	report callback is a convenience function that
+	the <seealso marker="#formatters">formatter</seealso> can use
+	to convert the report to a format string and arguments. The
+	formatter can also use its own conversion function, if no
+	callback is provided, or if a customized formatting is
+	desired.</p>
+      <p>Example, format string and arguments:</p>
+      <code>logger:error("The file does not exist: ~ts",[Filename])</code>
+      <p>Example, string:</p>
+      <code>logger:notice("Something strange happened!")</code>
+      <p>Example, report, and metadata with report callback:</p>
+      <code>
+logger:debug(#{got => connection_request, id => Id, state => State},
+             #{report_cb => fun(R) -> {"~p",[R]} end})</code>
+      <p>The log message can also be provided through a fun for lazy
+	evaluation. The fun is only evaluated if the global log level
+	check passes, and is therefore recommended if it is expensive
+	to generate the message. The lazy fun must return a string, a
+	report, or a tuple with format string and arguments.</p>
+    </section>
+    <section>
+      <title>Metadata</title>
+      <p>Metadata contains additional data associated with a log
+	message. Logger inserts some metadata fields by default, and
+	the client can add custom metadata in two different ways:</p>
       <taglist>
-	<tag><marker id="Handler"/>Handler</tag>
+	<tag>Set process metadata</tag>
 	<item>
-	  <p>A handler is defined as a module exporting the following
-	    function:</p>
-
-	  <code>log(Log, Config) -> ok</code>
-
-	  <p>A handler is called by the logger backend after filtering on
-	    logger level and on handler level for the handler which is
-	    about to be called. The function call is done on the client
-	    process, and it is up to the handler implementation if other
-	    processes are to be involved or not.</p>
-
-	  <p>Multiple instances of the same handler can be
-	    added. Configuration is per instance.</p>
-
+	  <p>Process metadata is set and updated
+	    with <seealso marker="logger#set_process_metadata-1">
+	      <c>logger:set_process_metadata/1</c></seealso>
+	    and <seealso marker="logger#update_process_metadata-1">
+	      <c>logger:update_process metadata/1</c></seealso>,
+	    respectively. This metadata applies to the process on
+	    which these calls are made, and Logger adds the metadata
+	    to all log events issued on that process.</p>
 	</item>
-
-	<tag><marker id="Filter"/>Filter</tag>
-	<item>
-	  <p>Filters can be set on the logger or on a handler. Logger
-	    filters are applied first, and if passed, the handler filters
-	    for each handler are applied. The handler callback is only
-	    called if all handler filters for the handler in question also
-	    pass.</p>
-
-	  <p>A filter is specified as:</p>
-
-	  <code>{fun((Log,Extra) -> Log | stop | ignore), Extra}</code>
-
-	  <p>The configuration parameter <c>filter_default</c>
-	    specifies the behavior if all filters return <c>ignore</c>.
-	    <c>filter_default</c> is by default set to <c>log</c>.</p>
-
-	  <p>The <c>Extra</c> parameter may contain any data that the
-	    filter needs.</p>
-	</item>
-
-	<tag><marker id="Formatter"/>Formatter</tag>
+	<tag>Add metadata to a specifc log event</tag>
 	<item>
-	  <p>A formatter is defined as a module exporting the following
-	    function:</p>
-
-	  <code>format(Log,Extra) -> unicode:chardata()</code>
-
-	  <p>The formatter callback is called by each handler, and the
-	    returned string can be printed to the handler's destination
-	    (stdout, file, ...).</p>
+	  <p>Metadata associated with one specifc log event is given
+	    as the last parameter to the log macro or Logger API
+	    function when the event is issued. For example:</p>
+	  <code>?LOG_ERROR("Connection closed",#{context => server})</code>
 	</item>
-
       </taglist>
+      <p>See the description of
+	the <seealso marker="logger#type-metadata">
+	  <c>logger:metadata()</c></seealso> type for information
+	about which default keys Logger inserts, and how the different
+	metadata maps are merged.</p>
     </section>
+  </section>
+  <section>
+    <marker id="filter"/>
+    <title>Filters</title>
+    <p>Filters can be global, or attached to a specific
+      handler. Logger calls the global filters first, and if they all
+      pass, it calls the handler filters for each handler. Logger
+      calls the handler callback only if all filters attached to the
+      handler in question also pass.</p>
+    <p>A filter is defined as:</p>
+    <pre>{FilterFun, Extra}</pre>
+    <p>where <c>FilterFun</c> is a function of arity 2,
+      and <c>Extra</c> is any term. When applying the filter, Logger
+      calls the function with the log event as the first argument,
+      and the value of <c>Extra</c> as the second
+      argument. See <seealso marker="logger#type-filter">
+	<c>logger:filter()</c></seealso> for type definitions.</p>
+    <p>The filter function can return <c>stop</c>, <c>ignore</c> or
+      the (possibly modified) log event.</p>
+    <p>If <c>stop</c> is returned, the log event is immediately
+      discarded. If the filter is global, no handler filters or
+      callbacks are called. If it is a handler filter, the
+      corresponding handler callback is not called, but the log event
+      is forwarded to filters attached to the next handler, if
+      any.</p>
+    <p>If the log event is returned, the next filter function is
+      called with the returned value as the first argument. That is,
+      if a filter function modifies the log event, the next filter
+      function receives the modified event. The value returned from
+      the last filter function is the value that the handler callback
+      receives.</p>
+    <p>If the filter function returns <c>ignore</c>, it means that it
+      did not recognize the log event, and thus leaves to other
+      filters to decide the event's destiny.</p>
+    <p>The configuration
+      option <seealso marker="#filter_default"><c>filter_default</c></seealso>
+      specifies the behaviour if all filter functions
+      return <c>ignore</c>, or if no filters
+      exist. <c>filter_default</c> is by default set to <c>log</c>,
+      meaning that if all existing filters ignore a log event, Logger
+      forwards the event to the handler
+      callback. If <c>filter_default</c> is set to <c>stop</c>, Logger
+      discards such events.</p>
+    <p>Global filters are added
+      with <seealso marker="logger#add_logger_filter-2">
+	<c>logger:add_logger_filter/2</c></seealso>
+      and removed
+      with <seealso marker="logger#remove_logger_filter-1">
+	<c>logger:remove_logger_filter/1</c></seealso>. They can also
+      be added at system start via the Kernel configuration
+      parameter <seealso marker="#logger"><c>logger</c></seealso>.</p>
+    <p>Handler filters are added
+      with <seealso marker="logger#add_handler_filter-3">
+	<c>logger:add_handler_filter/3</c></seealso>
+      and removed
+      with <seealso marker="logger#remove_handler_filter-2">
+	<c>logger:remove_handler_filter/2</c></seealso>. They can also
+      be specified directly in the configuration when adding a handler
+      with <seealso marker="logger#add_handler/3">
+	<c>logger:add_handler/3</c></seealso>
+      or via the Kernel configuration
+      parameter <seealso marker="#logger"><c>logger</c></seealso>.</p>
+
+    <p>To see which filters are currently installed in the system,
+      use <seealso marker="logger#i-0"><c>logger:i/0</c></seealso>,
+      or <seealso marker="logger#get_logger_config-0">
+	<c>logger:get_logger_config/0</c></seealso>
+      and <seealso marker="logger#get_handler_config-1">
+	<c>logger:get_handler_config/1</c></seealso>. Filters are
+	listed in the order they are applied, that is, the first
+	filter in the list is applied first, and so on.</p>
+
+    <p>For convenience, the following built-in filters exist:</p>
 
-    <section>
-      <title>Built-in handlers</title>
-
-      <taglist>
-	<tag><c>logger_std_h</c></tag>
+    <taglist>
+	<tag><seealso marker="logger_filters#domain-2">
+	    <c>logger_filters:domain/2</c></seealso></tag>
 	<item>
-	  <p>This is the default handler used by OTP. Multiple instances
-	    can be started, and each instance will write log events to a
-	    given destination, console or file. Filters can be used for
-	    selecting which event to send to which handler instance.</p>
+	  <p>Provides a way of filtering log events based on a
+	  <c>domain</c> field in <c>Metadata</c>.</p>
 	</item>
-
-	<tag><c>logger_disk_log_h</c></tag>
+	<tag><seealso marker="logger_filters#level-2">
+	  <c>logger_filters:level/2</c></seealso></tag>
 	<item>
-	  <p>This handler behaves much like logger_std_h, except it uses
-	    <seealso marker="disk_log"><c>disk_log</c></seealso> as its
-	    destination.</p>
+	  <p>Provides a way of filtering log events based on the log
+	    level.</p>
 	</item>
-
-	<tag><marker id="ErrorLoggerManager"/><c>error_logger</c></tag>
+	<tag><seealso marker="logger_filters#progress-2">
+	    <c>logger_filters:progress/2</c></seealso></tag>
 	<item>
-	  <p>This handler is to be used for backwards compatibility
-	    only. It is not started by default, but will be automatically
-	    started the first time an event handler is added
-	    with <seealso marker="error_logger#add_report_handler-1">
-	      <c>error_logger:add_report_handler/1,2</c></seealso>.</p>
-
-	  <p>No built-in event handlers exist.</p>
+	  <p>Stops or allows progress reports from <c>supervisor</c>
+	    and <c>application_controller</c>.</p>
 	</item>
-      </taglist>
-    </section>
-
-    <section>
-      <title>Built-in filters</title>
-
-      <taglist>
-	<tag><c>logger_filters:domain/2</c></tag>
+	<tag><seealso marker="logger_filters#remote_gl-2">
+	    <c>logger_filters:remote_gl/2</c></seealso></tag>
 	<item>
-	  <p>This filter provides a way of filtering log events based on a
-	    <c>domain</c> field <c>Metadata</c>. See 
-	    <seealso marker="logger_filters#domain-2">
-	    <c>logger_filters:domain/2</c></seealso></p>
+	  <p>Stops or allows log events originating from a process
+	    that has its group leader on a remote node.</p>
 	</item>
+    </taglist>
+  </section>
 
-	<tag><c>logger_filters:level/2</c></tag>
-	<item>
-	  <p>This filter provides a way of filtering log events based
-	    on the log level. See <seealso marker="logger_filters#level-2">
-	    <c>logger_filters:level/2</c></seealso></p>
-	</item>
+  <section>
+    <marker id="handlers"/>
+    <title>Handlers</title>
+    <p>A handler is defined as a module exporting at least the
+      following function:</p>
+
+    <pre><seealso marker="logger#HModule:log-2">log(LogEvent, Config) -> void()</seealso></pre>
+
+    <p>This function is called when a log event has passed through all
+      global filters, and all handler filters attached to the handler
+      in question. The function call is executed on the client
+      process, and it is up to the handler implementation if other
+      processes are involved or not.</p>
+
+    <p>Logger allows adding multiple instances of a handler
+      callback. That is, if a callback module implementation allows
+      it, you can add multiple handler instances using the same
+      callback module. The different instances are identified by
+      unique handler identities.</p>
+
+    <p>In addition to the mandatory callback function <c>log/2</c>, a
+      handler module can export the optional callback
+      functions <c>adding_handler/1</c>, <c>changing_config/2</c>
+      and <c>removing_handler/1</c>. See
+      section <seealso marker="logger#handler_callback_functions">Handler
+      Callback Functions</seealso> in the logger(3) manual for more
+      information about these function.</p>
+
+    <p>The following built-in handlers exist:</p>
 
-	<tag><c>logger_filters:progress/2</c></tag>
-	<item>
-	  <p>This filter matches all progress reports
-	    from <c>supervisor</c> and <c>application_controller</c>.
-	    See <seealso marker="logger_filters#progress/2">
-	    <c>logger_filters:progress/2</c></seealso></p>
-	</item>
+    <taglist>
+      <tag><c>logger_std_h</c></tag>
+      <item>
+	<p>This is the default handler used by OTP. Multiple instances
+	  can be started, and each instance will write log events to a
+	  given destination, terminal or file.</p>
+      </item>
 
-	<tag><c>logger_filters:remote_gl/2</c></tag>
-	<item>
-	  <p>This filter matches all events originating from a process
-	    that has its group leader on a remote node.
-	    See <seealso marker="logger_filters#remote_gl/2">
-	    <c>logger_filters:remote_gl/2</c></seealso></p>
-	</item>
-      </taglist>
-    </section>
+      <tag><c>logger_disk_log_h</c></tag>
+      <item>
+	<p>This handler behaves much like <c>logger_std_h</c>, except it uses
+	  <seealso marker="disk_log"><c>disk_log</c></seealso> as its
+	  destination.</p>
+      </item>
 
-    <section>
-      <title>Default formatter</title>
+      <tag><marker id="ErrorLoggerManager"/><c>error_logger</c></tag>
+      <item>
+	<p>This handler is provided for backwards compatibility
+	  only. It is not started by default, but will be
+	  automatically started the first time an <c>error_logger</c>
+	  event handler is added
+	  with <seealso marker="error_logger#add_report_handler-1">
+	    <c>error_logger:add_report_handler/1,2</c></seealso>.</p>
+
+	<p>The old <c>error_logger</c> event handlers in STDLIB and
+	  SASL still exist, but they are not added by Erlang/OTP 21.0
+	  or later.</p>
+      </item>
+    </taglist>
+  </section>
 
-      <p>The default formatter is <c>logger_formatter</c>.
-	See <seealso marker="logger_formatter#format-2">
-	  <c>logger_formatter:format/2</c></seealso>.</p>
-    </section>
+  <section>
+    <marker id="formatters"/>
+    <title>Formatters</title>
+    <p>A formatter can be used by the handler implementation to do the
+      final formatting of a log event, before printing to the
+      handler's destination. The handler callback receives the
+      formatter information as part of the handler configuration,
+      which is passed as the second argument
+      to <seealso marker="logger#HModule:log-2">
+	<c>HModule:log/2</c></seealso>.</p>
+    <p>The formatter information consits of a formatter
+      module, <c>FModule</c> and its
+      configuration, <c>FConfig</c>. <c>FModule</c> must export the
+      following function, which can be called by the handler:</p>
+    <pre><seealso marker="logger#FModule:format-2">format(LogEvent,FConfig)
+	-> FormattedLogEntry</seealso></pre>
+    <p>The formatter information for a handler is set as a part of its
+      configuration when the handler is added. It can also be changed
+      during runtime
+      with <seealso marker="logger#set_handler_config-3">
+	<c>logger:set_handler_config(HandlerId,formatter,{FModule,FConfig})</c>
+      </seealso>, which overwrites the current formatter information,
+      or with <seealso marker="logger#update_formatter_config-2">
+	<c>logger:update_formatter_config/2,3</c></seealso>, which
+	only modifies the formatter configuration.</p>
+    <p>If the formatter module exports the optional callback
+      function <seealso marker="logger#FModule:check_config-1">
+	<c>check_config(FConfig)</c></seealso>, Logger calls this
+      function when the formatter information is set or modified, to
+      verify the validity of the formatter configuration.</p>
+    <p>If no formatter information is specified for a handler, Logger
+      uses <seealso marker="logger_formatter">
+	<c>logger_formatter(3)</c></seealso> as default.</p>
   </section>
 
   <section>
@@ -250,52 +434,58 @@
 
     <p>Logger can be configured either when the system starts through
       <seealso marker="config">configuration parameters</seealso>,
-      or at run-time by using the <seealso marker="logger">logger</seealso>
+      or at run-time by using the <seealso marker="logger">logger(3)</seealso>
       API. The recommended approach is to do the initial configuration in
       the <c>sys.config</c> file and then use the API when some configuration
-      has to be changed at run-time, such as the logging level.</p>
+      has to be changed at runtime, such as the log level.</p>
 
     <section>
-      <title>Application configuration parameters</title>
+      <title>Kernel Configuration Parameters</title>
       <p>Logger is best configured by using the configuration parameters
-      of kernel. There are three possible configuration parameters:
+      of Kernel. There are four possible configuration parameters:
       <seealso marker="#logger"><c>logger</c></seealso>,
       <seealso marker="kernel_app#logger_level"><c>logger_level</c></seealso>,
       <seealso marker="kernel_app#logger_sasl_compatible"><c>logger_sasl_compatible</c></seealso> and
-      <seealso marker="kernel_app#logger_log_progress"><c>logger_log_progress</c></seealso>.
-      logger_level, logger_sasl_compatible and logger_log_progress are described in the
+      <seealso marker="kernel_app#logger_progress_reports"><c>logger_progress_reports</c></seealso>.
+      <c>logger_level</c>, <c>logger_sasl_compatible</c> and <c>logger_progress_reports</c> are described in the
       <seealso marker="kernel_app#configuration">Kernel Configuration</seealso>,
       while <c>logger</c> is described below.</p>
-      <section>
+
         <marker id="logger"/>
-        <title>logger</title>
-        <p>The <c>logger</c> application configuration parameter is used to configure
-          three different logger aspects; handlers, logger filters and module levels.
+        <p><em>logger</em></p>
+        <p>The application configuration parameter <c>logger</c> is used to configure
+          three different Logger aspects; handlers, logger filters and module levels.
           The configuration is a list containing tagged tuples that look like this:</p>
         <taglist>
           <tag><c>DisableHandler = {handler,default,undefined}</c></tag>
-          <item>Disable the default handler. This will allow another application
+          <item>
+	    <p>Disable the default handler. This allows another application
             to add its own default handler. See <seealso marker="logger#add_handlers/1">
-            <c>logger:add_handlers/1</c></seealso> for more details.</item>
+            <c>logger:add_handlers/1</c></seealso> for more details.</p>
+	    <p>Only one entry of this option is allowed.</p></item>
           <tag><c>AddHandler = {handler,HandlerId,Module,HandlerConfig}</c></tag>
-          <item>Add a handler as if <seealso marker="logger:add_handler/3">
-            <c>logger:add_handler(HandlerId,Module,HandlerConfig)</c></seealso> had been
-            called.</item>
-          <tag><c>Filters = {filters, FilterDefault, [Filter]}</c><br/>
+          <item>
+	    <p>Add a handler as if <seealso marker="logger:add_handler/3">
+            <c>logger:add_handler(HandlerId,Module,HandlerConfig)</c></seealso> is
+            called.</p>
+	    <p>It is allowed to have multiple entries of this option.</p></item>
+          <tag><c>Filters = {filters, default, [Filter]}</c><br/>
           <c>FilterDefault = log | stop</c><br/>
           <c>Filter = {FilterId, {FilterFun, FilterConfig}}</c></tag>
-          <item>Add the specified <seealso marker="logger#add_logger_filter/2">
-          logger filters</seealso>. Only one entry is allowed of this option.</item>
-          <tag><c>ModuleLevel</c></tag>
-          <item><c>{module_level, Level, [Module]}</c>,
-            this option configures the <seealso marker="logger#set_module_level/2">
-            module log level</seealso> to be used. It is possible to have multiple
-            <c>module_level</c> entries.</item>
+          <item>
+	    <p>Add the specified <seealso marker="logger#add_logger_filter/2">
+            logger filters</seealso>.</p>
+	    <p>Only one entry of this option is allowed.</p></item>
+          <tag><c>ModuleLevel = {module_level, Level, [Module]}</c></tag>
+          <item>
+	    <p>This option configures <seealso marker="logger#set_module_level/2">
+            module log level</seealso>.</p>
+	    <p>It is allowed to have multiple entries of this option.</p></item>
         </taglist>
         <p>Examples:</p>
         <list>
           <item>
-          <p>Output logs into a the file &quot;logs/erlang.log&quot;</p>
+          <p>Output logs into the file &quot;logs/erlang.log&quot;</p>
             <code>
 [{kernel,
   [{logger,
@@ -338,153 +528,175 @@
             </code>
           </item>
         </list>
-      </section>
     </section>
 
     <section>
-      <title>Logger configuration</title>
+      <title>Global Logger Configuration</title>
 
       <taglist>
-	<tag><c>level</c></tag>
+	<tag><c>level = </c><seealso marker="logger#type-level">
+	    <c>logger:level()</c></seealso></tag>
 	<item>
-	  <p>Specifies the severity level to log.</p>
+	  <p>Specifies the global log level to log.</p>
+	  <p>See section <seealso marker="#log_level">Log
+	      Level</seealso> for a listing and description of
+	      possible log levels.</p>
+	  <p>The initial value of this option is set by the Kernel
+	    configuration
+	    parameter <seealso marker="kernel_app#logger_level">
+	      <c>logger_level</c></seealso>. It can be changed during
+	      runtime
+	      with <seealso marker="logger#set_logger_config-2">
+	      <c>logger:set_logger_config(level,NewLevel)</c></seealso>.</p>
 	</item>
-	<tag><c>filters</c></tag>
+	<tag><c>filters = [{</c><seealso marker="logger#type-filter_id">
+	    <c>logger:filter_id()</c></seealso><c>,</c>
+	  <seealso marker="logger#type-filter">
+	    <c>logger:filter()</c></seealso><c>}]</c></tag>
 	<item>
-	  <p>Logger filters are added or removed with
+	  <p>Global filters are added and removed with
 	    <seealso marker="logger#add_logger_filter-2">
 	      <c>logger:add_logger_filter/2</c></seealso> and
 	    <seealso marker="logger#remove_logger_filter-1">
 	      <c>logger:remove_logger_filter/1</c></seealso>,
 	    respectively.</p>
-	  <p>See <seealso marker="#Filter">Filter</seealso> for more
-	    information.</p>
-	  <p>By default, no filters exist.</p>
+	  <p>See section <seealso marker="#filters">Filters</seealso>
+	    for more information.</p>
+	  <p>Default is <c>[]</c>, that is, no filters exist.</p>
 	</item>
-	<tag><c>filter_default = log | stop</c></tag>
+	<tag><marker id="filter_default"/><c>filter_default = log | stop</c></tag>
 	<item>
 	  <p>Specifies what to do with an event if all filters
-	    return <c>ignore</c>.</p>
+	    return <c>ignore</c>, or if no filters exist.</p>
+	  <p>See section <seealso marker="#filters">Filters</seealso>
+	    for more information about how this option is used.</p>
 	  <p>Default is <c>log</c>.</p>
 	</item>
-	<tag><c>handlers</c></tag>
-	<item>
-	  <p>Handlers are added or removed with
-	    <seealso marker="logger#add_handler-3">
-	      <c>logger:add_handler/3</c></seealso> and
-	    <seealso marker="logger#remove_handler-1">
-	      <c>logger:remove_handler/1</c></seealso>,
-	    respectively.</p>
-	  <p>See <seealso marker="#Handler">Handler</seealso> for more
-	    information.</p>
-	</item>
       </taglist>
     </section>
 
     <section>
       <marker id="handler_configuration"/>
-      <title>Handler configuration</title>
+      <title>Handler Configuration</title>
       <taglist>
-	<tag><c>level</c></tag>
+	<tag><c>level = </c><seealso marker="logger#type-level">
+	    <c>logger:level()</c></seealso></tag>
 	<item>
-	  <p>Specifies the severity level to log.</p>
+	  <p>Specifies the log level which the handler logs.</p>
+	  <p>See section <seealso marker="#log_level">Log
+	      Level</seealso> for a listing and description of
+	      possible log levels.</p>
+	  <p>The log level can be specified when adding the handler,
+	    or changed during runtime with, for
+	    instance, <seealso marker="logger#set_handler_config/3">
+	      <c>logger:set_handler_config/3</c></seealso>.</p>
+	  <p>Default is <c>info</c>.</p>
 	</item>
-	<tag><c>filters</c></tag>
+	<tag><c>filters = [{</c><seealso marker="logger#type-filter_id">
+	    <c>logger:filter_id()</c></seealso><c>,</c>
+	  <seealso marker="logger#type-filter">
+	    <c>logger:filter()</c></seealso><c>}]</c></tag>
 	<item>
 	  <p>Handler filters can be specified when adding the handler,
-	    or added or removed later with
+	    or added or removed during runtime with
 	    <seealso marker="logger#add_handler_filter-3">
 	      <c>logger:add_handler_filter/3</c></seealso> and
 	    <seealso marker="logger#remove_handler_filter-2">
 	      <c>logger:remove_handler_filter/2</c></seealso>,
 	    respectively.</p>
-	  <p>See <seealso marker="#Filter">Filter</seealso> for more
+	  <p>See <seealso marker="#filters">Filters</seealso> for more
 	    information.</p>
-	  <p>By default, no filters exist.</p>
+	  <p>Default is <c>[]</c>, that is, no filters exist.</p>
 	</item>
-	<tag><c>filter_default = log | stop</c></tag>
+	<tag><marker id="filter_default"/><c>filter_default = log | stop</c></tag>
 	<item>
 	  <p>Specifies what to do with an event if all filters
-	    return <c>ignore</c>.</p>
+	    return <c>ignore</c>, or if no filters exist.</p>
+	  <p>See section <seealso marker="#filters">Filters</seealso>
+	    for more information about how this option is used.</p>
 	  <p>Default is <c>log</c>.</p>
 	</item>
-	<tag><c>formatter = {Module::module(),Extra::term()}</c></tag>
+	<tag><c>formatter = {module(),</c><seealso marker="logger#type-formatter_config">
+	    <c>logger:formatter_config()</c></seealso><c>}</c></tag>
 	<item>
-	  <p>See <seealso marker="#Formatter">Formatter</seealso> for more
+	  <p>The formatter which the handler can use for converting
+	    the log event term to a printable string.</p>
+	  <p>See <seealso marker="#formatters">Formatters</seealso> for more
 	    information.</p>
-	  <p>The default module is <seealso marker="logger_formatter">
-	      <c>logger_formatter</c></seealso>, and <c>Extra</c> is
-	      it's configuration map.</p>
+	  <p>Default
+	    is <c>{logger_formatter,DefaultFormatterConfig}</c>, see
+	    the <seealso marker="logger_formatter">
+	      <c>logger_formatter(3)</c></seealso>
+	    manual for information about this formatter and its
+	    default configuration.</p>
 	</item>
-        <tag>HandlerConfig, <c>term() = term()</c></tag>
+        <tag><c>HandlerConfig, atom() = term()</c></tag>
         <item>
-          Any keys not listed above are considered to be handler specific
-          configuration. The configuration of the Kernel handlers can be found in
-          <seealso marker="logger_std_h"><c>logger_std_h</c></seealso> and
-          <seealso marker="logger_disk_log_h"><c>logger_disk_log_h</c></seealso>.
+          <p>Any keys not listed above are considered to be handler
+            specific configuration. The configuration of the Kernel
+            handlers can be found in
+            the <seealso marker="logger_std_h"><c>logger_std_h(3)</c></seealso>
+            and
+            <seealso marker="logger_disk_log_h"><c>logger_disk_log_h(3)</c>
+	    </seealso> manual pages.</p>
         </item>
       </taglist>
 
-      <p>Note that <c>level</c> and <c>filters</c> are obeyed by
+      <p>Notice that <c>level</c> and <c>filters</c> are obeyed by
 	Logger itself before forwarding the log events to each
-	handler, while <c>formatter</c> is left to the handler
-	implementation. All Logger's built-in handlers will call the
-	given formatter before printing.</p>
+	handler, while <c>formatter</c> and all handle specific
+	options are left to the handler implementation.</p>
+      <p>All Logger's built-in handlers will call the given formatter
+	before printing.</p>
     </section>
 
   </section>
 
   <section>
     <marker id="compatibility"/>
-    <title>Backwards compatibility with error_logger</title>
-    <p>Logger provides backwards compatibility with the old
+    <title>Backwards Compatibility with error_logger</title>
+    <p>Logger provides backwards compatibility with
       <c>error_logger</c> in the following ways:</p>
 
     <taglist>
-      <tag>Legacy event handlers</tag>
-      <item>
-	<p>To use event handlers written for <c>error_logger</c>, just
-	  add your event handler with</p>
-	<code>
-error_logger:add_report_handler/1,2.
-	</code>
-	<p>This will automatically start the <c>error_logger</c>
-	  event manager, and add <c>error_logger</c> as a
-	  handler to <c>logger</c>, with configuration</p>
-<code>
-#{level=>info,
-  filter_default=>log,
-  filters=>[]}.
-</code>
-	<p>Note that this handler will ignore events that do not
-	  originate from the old <c>error_logger</c> API, or from
-	  within OTP. This means that if your code uses the logger API
-	  for logging, then your log events will be discarded by this
-	  handler.</p>
-	<p>Also note that <c>error_logger</c> is not overload
-	  protected.</p>
-      </item>
-      <tag>Logger API</tag>
+      <tag>API for Logging</tag>
       <item>
-	<p>The old <c>error_logger</c> API still exists, but should
-	  only be used by legacy code. It will be removed in a later
+	<p>The <c>error_logger</c> API still exists, but should only
+	  be used by legacy code. It will be removed in a later
 	  release.</p>
+	<p>Calls
+	  to <seealso marker="error_logger#error_report-1">
+	    <c>error_logger:error_report/1,2</c></seealso>,
+	  <seealso marker="error_logger#error_msg-1">
+	    <c>error_logger:error_msg/1,2</c></seealso>, and
+	  corresponding functions for warning and info messages, are
+	  all forwarded to Logger as calls
+	  to <seealso marker="logger#log-3">
+	    <c>logger:log(Level,Report,Metadata)</c></seealso>.</p>
+	<p><c>Level = error | warning | info</c> and is taken
+	  from the function name. <c>Report</c> contains the actual
+	  log message, and <c>Metadata</c> contains additional
+	  information which can be used for creating backwards
+	  compatible events for legacy <c>error_logger</c> event
+	  handlers, see
+	  section <seealso marker="#legacy_event_handlers">Legacy
+	  Event Handlers</seealso>.</p>
       </item>
-      <tag>Output format</tag>
+      <tag>Output Format</tag>
       <item>
 	<p>To get log events on the same format as produced
 	  by <c>error_logger_tty_h</c> and <c>error_logger_file_h</c>,
 	  use the default formatter, <c>logger_formatter</c>, with
-	  configuration parameter <c>legacy_header=>true</c>. This is
+	  configuration parameter <c>legacy_header => true</c>. This is
 	  also the default.</p>
       </item>
-      <tag>Default format of log events from OTP</tag>
+      <tag>Default Format of Log Events from OTP</tag>
       <item>
 	<p>By default, all log events originating from within OTP,
 	  except the former so called "SASL reports", look the same as
 	  before.</p>
       </item>
-      <tag>SASL reports</tag>
+      <tag><marker id="sasl_reports"/>SASL Reports</tag>
       <item>
 	<p>By SASL reports we mean supervisor reports, crash reports
 	  and progress reports.</p>
@@ -494,96 +706,134 @@ error_logger:add_report_handler/1,2.
 	  named <c>sasl_report_tty_h</c>
 	  and <c>sasl_report_file_h</c>.</p>
 	<p>The destination of these log events were configured by
-	  environment variables for the SASL application.</p>
+	  <seealso marker="sasl:sasl_app#deprecated_error_logger_config">SASL
+	  configuration parameters</seealso>.</p>
 	<p>Due to the specific event handlers, the output format
 	  slightly differed from other log events.</p>
-	<p>As of OTP-21, the concept of SASL reports is removed,
-	  meaning that the default behavior is as follows:</p>
+	<p>As of Erlang/OTP 21.0, the concept of SASL reports is
+	  removed, meaning that the default behaviour is as
+	  follows:</p>
 	<list>
-	  <item>Supervisor reports, crash reports and progress reports
+	  <item>Supervisor reports, crash reports, and progress reports
 	    are no longer connected to the SASL application.</item>
 	  <item>Supervisor reports and crash reports are logged by
 	    default.</item>
 	  <item>Progress reports are not logged by default, but can be
-	    enabled with the kernel environment
-	    variable <c>logger_log_progress</c>.</item>
+	    enabled with the Kernel configuration
+	    parameter <seealso marker="kernel_app#logger_progress_reports">
+	    <c>logger_progress_reports</c></seealso>.</item>
 	  <item>The output format is the same for all log
 	    events.</item>
 	</list>
-	<p>If the old behavior is preferred, the kernel environment
-	  variable <c>logger_sasl_compatible</c> can be set
-	  to <c>true</c>. The old SASL environment variables can then
-	  be used as before, and the SASL reports will only be printed
-	  if the SASL application is running - through a second log
-	  handler named <c>sasl_h</c>.</p>
+	<p>If the old behaviour is preferred, the Kernel configuation
+	  parameter <seealso marker="kernel_app:logger_sasl_compatible">
+	    <c>logger_sasl_compatible</c></seealso> can be set
+	  to <c>true</c>. The
+	  <seealso marker="sasl:sasl_app#deprecated_error_logger_config">SASL
+	  configuration parameters</seealso> can then be used as
+	  before, and the SASL reports will only be printed if the
+	  SASL application is running, through a second log handler
+	  named <c>sasl</c>.</p>
 	<p>All SASL reports have a metadata
-	  field <c>domain=>[beam,erlang,otp,sasl]</c>, which can be
+	  field <c>domain => [beam,erlang,otp,sasl]</c>, which can be
 	  used, for example, by filters to stop or allow the
-	  events.</p>
+	  log events.</p>
+	<p>See the <seealso marker="sasl:error_logging">SASL User's
+	  Guide</seealso> for more information about the old SASL
+	  error logging functionality.</p>
+      </item>
+      <tag><marker id="legacy_event_handlers"/>Legacy Event Handlers</tag>
+      <item>
+	<p>To use event handlers written for <c>error_logger</c>, just
+	  add your event handler with</p>
+	<code>
+error_logger:add_report_handler/1,2.
+	</code>
+	<p>This will automatically start the <c>error_logger</c>
+	  event manager, and add <c>error_logger</c> as a
+	  handler to <c>logger</c>, with configuration</p>
+<code>
+#{level => info,
+  filter_default => log,
+  filters => []}.
+</code>
+	<p>Notice that this handler will ignore events that do not
+	  originate from the <c>error_logger</c> API, or from within
+	  OTP. This means that if your code uses the Logger API for
+	  logging, then your log events will be discarded by this
+	  handler.</p>
+	<p>Also notice that <c>error_logger</c> is not overload
+	  protected.</p>
       </item>
     </taglist>
   </section>
 
 
   <section>
-    <title>Error handling</title>
+    <title>Error Handling</title>
     <p>Log data is expected to be either a format string and
-      arguments, a string (unicode:chardata), or a report (map or
+      arguments, a string
+      (<seealso marker="stdlib:unicode#type-chardata">
+	<c>unicode:chardata()</c></seealso>), or a report (map or
       key-value list) which can be converted to a format string and
-      arguments by the handler. A default report callback should be
-      included in the log event's metadata, which can be used for
-      converting the report to a format string and arguments. The
-      handler might also do a custom conversion if the default format
-      is not desired.</p>
-    <p><c>logger</c> does, to a certain extent, check its input data
+      arguments by the handler. If a report is given, a default report
+      callback can be included in the log event's metadata. The
+      handler can use this callback for converting the report to a
+      format string and arguments. If the format obtained by the
+      provided callback is not desired, or if there is no provided
+      callback, the handler must do a custom conversion.</p>
+    <p>Logger does, to a certain extent, check its input data
       before forwarding a log event to the handlers, but it does not
       evaluate conversion funs or check the validity of format strings
       and arguments. This means that any filter or handler must be
       careful when formatting the data of a log event, making sure
       that it does not crash due to bad input data or faulty
       callbacks.</p>
-    <p>If a filter or handler still crashes, logger will remove the
-      filter or handler in question from the configuration, and then
-      print a short error message on the console. A debug event
-      containing the crash reason and other details is also issued,
-      and can be seen if a handler is installed which logs on debug
-      level.</p>
+    <p>If a filter or handler still crashes, Logger will remove the
+      filter or handler in question from the configuration, and print
+      a short error message to the terminal. A debug event containing
+      the crash reason and other details is also issued, and can be
+      seen if a handler logging debug events is installed.</p>
   </section>
 
   <section>
     <title>Example: add a handler to log debug events to file</title>
-    <p>When starting an erlang node, the default behavior is that all
+    <p>When starting an Erlang node, the default behaviour is that all
       log events with level info and above are logged to the
-      console. In order to also log debug events, you can either
+      terminal. In order to also log debug events, you can either
       change the global log level to <c>debug</c> or add a separate
       handler to take care of this. In this example we will add a new
       handler which prints the debug events to a separate file.</p>
-    <p>First, we add an instance of logger_std_h with
+    <p>First, we add an instance of <c>logger_std_h</c> with
       type <c>{file,File}</c>, and we set the handler's level
       to <c>debug</c>:</p>
     <pre>
-1> <input>Config = #{level=>debug,logger_std_h=>#{type=>{file,"./debug.log"}}}.</input>
+1> <input>Config = #{level => debug, logger_std_h => #{type => {file,"./debug.log"}}}.</input>
 #{logger_std_h => #{type => {file,"./debug.log"}},
   level => debug}
 2> <input>logger:add_handler(debug_handler,logger_std_h,Config).</input>
 ok</pre>
     <p>By default, the handler receives all events
-      (<c>filter_defalt=log</c>), so we need to add a filter to stop
-      all non-debug events:</p>
+      (<c>filter_default=log</c>, see
+      section <seealso marker="#filters">Filters</seealso> for more
+      details), so we need to add a filter to stop all non-debug
+      events. The built-in
+      filter <seealso marker="logger_filters#level-2">
+	<c>logger_filters:level/2</c></seealso>
+      is used for this:</p>
     <pre>
-3> <input>Fun = fun(#{level:=debug}=Log,_) -> Log; (_,_) -> stop end.</input>
-#Fun&lt;erl_eval.12.98642416>
-4> <input>logger:add_handler_filter(debug_handler,allow_debug,{Fun,[]}).</input>
+3> <input>logger:add_handler_filter(debug_handler,stop_non_debug,
+                             {fun logger_filters:level/2,{stop,neq,debug}}).</input>
 ok</pre>
-    <p>And finally, we need to make sure that the logger itself allows
+    <p>And finally, we need to make sure that Logger itself allows
       debug events. This can either be done by setting the global
-      logger level:</p>
+      log level:</p>
     <pre>
-5> <input>logger:set_logger_config(level,debug).</input>
+4> <input>logger:set_logger_config(level,debug).</input>
 ok</pre>
     <p>Or by allowing debug events from one or a few modules only:</p>
     <pre>
-6> <input>logger:set_module_level(mymodule,debug).</input>
+5> <input>logger:set_module_level(mymodule,debug).</input>
 ok</pre>
 
   </section>
@@ -592,107 +842,112 @@ ok</pre>
     <title>Example: implement a handler</title>
     <p>The only requirement that a handler MUST fulfill is to export
       the following function:</p>
-    <code>log(logger:log(),logger:config()) ->ok</code>
-    <p>It may also implement the following callbacks:</p>
+    <code>log(logger:log_event(),logger:config()) -> ok</code>
+    <p>It can optionally also implement the following callbacks:</p>
     <code>
-adding_handler(logger:handler_id(),logger:config()) -> {ok,logger:config()} | {error,term()}
-removing_handler(logger:handler_id(),logger:config()) -> ok
-changing_config(logger:handler_id(),logger:config(),logger:config()) -> {ok,logger:config()} | {error,term()}
+adding_handler(logger:config()) -> {ok,logger:config()} | {error,term()}
+removing_handler(logger:config()) -> ok
+changing_config(logger:config(),logger:config()) -> {ok,logger:config()} | {error,term()}
     </code>
-    <p>When logger:add_handler(Id,Module,Config) is called, logger
-      will first call Module:adding_handler(Id,Config), and if it
-      returns {ok,NewConfig} the NewConfig is written to the
-      configuration database. After this, the handler may receive log
-      events as calls to Module:log/2.</p>
+    <p>When <c>logger:add_handler(Id,Module,Config)</c> is called,
+      Logger first calls <c>HModule:adding_handler(Config)</c>. If
+      this function returns <c>{ok,NewConfig}</c>, Logger
+      writes <c>NewConfig</c> to the configuration database, and
+      the <c>logger:add_handler/3</c> call returns. After this, the
+      handler is installed and must be ready to receive log events as
+      calls to <c>HModule:log/2</c>.</p>
     <p>A handler can be removed by calling
-      logger:remove_handler(Id). logger will call
-      Module:removing_handler(Id,Config), and then remove the handler's
-      configuration from the configuration database.</p>
-    <p>When logger:set_handler_config is called, logger calls
-      Module:changing_config(Id,OldConfig,NewConfig). If this function
-      returns ok, the NewConfig is written to the configuration
-      database.</p>
-
-    <p>A simple handler which prints to the console could be
-      implemented as follows:</p>
+      <c>logger:remove_handler(Id)</c>. Logger calls
+      <c>HModule:removing_handler(Config)</c>, and removes the
+      handler's configuration from the configuration database.</p>
+    <p>When <c>logger:set_handler_config/2,3</c>
+      or <c>logger:update_handler_config/2</c> is called, Logger
+      calls <c>HModule:changing_config(OldConfig,NewConfig)</c>. If
+      this function returns <c>{ok,NewConfig}</c>, Logger
+      writes <c>NewConfig</c> to the configuration database.</p>
+
+    <p>A simple handler that prints to the terminal can be implemented
+      as follows:</p>
     <code>
 -module(myhandler).
 -export([log/2]).
 
-log(Log,#{formatter:={FModule,FConfig}) ->
-    io:put_chars(FModule:format(Log,FConfig)).
+log(LogEvent,#{formatter:={FModule,FConfig}) ->
+    io:put_chars(FModule:format(LogEvent,FConfig)).
     </code>
 
     <p>A simple handler which prints to file could be implemented like
       this:</p>
     <code>
 -module(myhandler).
--export([adding_handler/2, removing_handler/2, log/2]).
+-export([adding_handler/1, removing_handler/1, log/2]).
 -export([init/1, handle_call/3, handle_cast/2, terminate/2]).
 
-adding_handler(Id,Config) ->
+adding_handler(Config) ->
     {ok,Fd} = file:open(File,[append,{encoding,utf8}]),
-    {ok,Config#{myhandler_fd=>Fd}}.
+    {ok,Config#{myhandler_fd => Fd}}.
 
-removing_handler(Id,#{myhandler_fd:=Fd}) ->
+removing_handler(#{myhandler_fd:=Fd}) ->
     _ = file:close(Fd),
     ok.
 
-log(Log,#{myhandler_fd:=Fd,formatter:={FModule,FConfig}}) ->
-    io:put_chars(Fd,FModule:format(Log,FConfig)).
+log(LogEvent,#{myhandler_fd:=Fd,formatter:={FModule,FConfig}}) ->
+    io:put_chars(Fd,FModule:format(LogEvent,FConfig)).
     </code>
 
     <note><p>The above handlers do not have any overload
       protection, and all log events are printed directly from the
       client process.</p></note>
 
-    <p>For examples of overload protection, please refer to the
-      implementation
-      of <seealso marker="logger_std_h"><c>logger_std_h</c></seealso>
-      and <seealso marker="logger_disk_log_h"><c>logger_disk_log_h</c>
+    <p>For information and examples of overload protection, please
+      refer to
+      section <seealso marker="#overload_protection">Protecting the
+      Handler from Overload</seealso>, and the implementation
+      of <seealso marker="logger_std_h"><c>logger_std_h(3)</c></seealso>
+      and <seealso marker="logger_disk_log_h"><c>logger_disk_log_h(3)</c>
       </seealso>.</p>
 
     <p>Below is a simpler example of a handler which logs through one
       single process.</p>
     <code>
 -module(myhandler).
--export([adding_handler/2, removing_handler/2, log/2]).
+-export([adding_handler/1, removing_handler/1, log/2]).
 -export([init/1, handle_call/3, handle_cast/2, terminate/2]).
 
-adding_handler(Id,Config) ->
+adding_handler(Config) ->
     {ok,Pid} = gen_server:start(?MODULE,Config),
-    {ok,Config#{myhandler_pid=>Pid}}.
+    {ok,Config#{myhandler_pid => Pid}}.
 
-removing_handler(Id,#{myhandler_pid:=Pid}) ->
+removing_handler(#{myhandler_pid:=Pid}) ->
     gen_server:stop(Pid).
 
-log(Log,#{myhandler_pid:=Pid} = Config) ->
-    gen_server:cast(Pid,{log,Log,Config}).
+log(LogEvent,#{myhandler_pid:=Pid} = Config) ->
+    gen_server:cast(Pid,{log,LogEvent,Config}).
 
 init(#{myhandler_file:=File}) ->
     {ok,Fd} = file:open(File,[append,{encoding,utf8}]),
-    {ok,#{file=>File,fd=>Fd}}.
+    {ok,#{file => File, fd => Fd}}.
 
 handle_call(_,_,State) ->
     {reply,{error,bad_request},State}.
 
-handle_cast({log,Log,Config},#{fd:=Fd} = State) ->
-    do_log(Fd,Log,Config),
+handle_cast({log,LogEvent,Config},#{fd:=Fd} = State) ->
+    do_log(Fd,LogEvent,Config),
     {noreply,State}.
 
 terminate(Reason,#{fd:=Fd}) ->
     _ = file:close(Fd),
     ok.
 
-do_log(Fd,Log,#{formatter:={FModule,FConfig}}) ->
-    String = FModule:format(Log,FConfig),
+do_log(Fd,LogEvent,#{formatter:={FModule,FConfig}}) ->
+    String = FModule:format(LogEvent,FConfig),
     io:put_chars(Fd,String).
     </code>
   </section>
 
   <section>
     <marker id="overload_protection"/>
-    <title>Protecting the handler from overload</title>
+    <title>Protecting the Handler from Overload</title>
     <p>In order for the built-in handlers to survive, and stay responsive,
     during periods of high load (i.e. when huge numbers of incoming
     log requests must be handled), a mechanism for overload protection
@@ -703,7 +958,7 @@ do_log(Fd,Log,#{formatter:={FModule,FConfig}}) ->
     as follows:</p>
     
     <section>
-      <title>Message queue length</title>
+      <title>Message Queue Length</title>
       <p>The handler process keeps track of the length of its message
       queue and reacts in different ways depending on the current status.
       The purpose is to keep the handler in, or (as quickly as possible),
@@ -720,7 +975,7 @@ do_log(Fd,Log,#{formatter:={FModule,FConfig}}) ->
 	  and as long as the length of the message queue is lower, all log
 	  requests are handled asynchronously. This simply means that the
 	  process sending the log request (by calling a log function in the
-	  logger API) does not wait for a response from the handler but
+	  Logger API) does not wait for a response from the handler but
 	  continues executing immediately after the request (i.e. it will not
 	  be affected by the time it takes the handler to print to the log
 	  device). If the message queue grows larger than this value, however,
@@ -798,14 +1053,14 @@ logger:add_handler(my_standard_h, logger_std_h,
     </section>
 
     <section>
-      <title>Controlling bursts of log requests</title>
+      <title>Controlling Bursts of Log Requests</title>
       <p>A potential problem with large bursts of log requests, is that log files
       may get full or wrapped too quickly (in the latter case overwriting
       previously logged data that could be of great importance). For this reason,
       both built-in handlers offer the possibility to set a maximum level of how
       many requests to process with a certain time frame. With this burst control
       feature enabled, the handler will take care of bursts of log requests
-      without choking log files, or the console, with massive amounts of
+      without choking log files, or the terminal, with massive amounts of
       printouts. These are the configuration parameters:</p>
       
       <taglist>
@@ -839,7 +1094,7 @@ logger:add_handler(my_disk_log_h, logger_disk_log_h,
     </section>
 
     <section>
-      <title>Terminating a large handler</title>
+      <title>Terminating a Large Handler</title>
       <p>A handler process may grow large even if it can manage peaks of high load
       without crashing. The overload protection mechanism includes user configurable
       levels for a maximum allowed message queue length and maximum allowed memory
@@ -876,7 +1131,14 @@ logger:add_handler(my_disk_log_h, logger_disk_log_h,
 
   <section>
     <title>See Also</title>
-    <p><seealso marker="error_logger"><c>error_logger(3)</c></seealso>,
-    <seealso marker="sasl:sasl_app"><c>SASL(6)</c></seealso></p>
+    <p>
+      <seealso marker="disk_log"><c>disk_log(3)</c></seealso>,
+      <seealso marker="error_logger"><c>error_logger(3)</c></seealso>,
+      <seealso marker="logger"><c>logger(3)</c></seealso>,
+      <seealso marker="logger_disk_log_h"><c>logger_disk_log_h(3)</c></seealso>,
+      <seealso marker="logger_filters"><c>logger_filters(3)</c></seealso>,
+      <seealso marker="logger_formatter"><c>logger_formatter(3)</c></seealso>,
+      <seealso marker="logger_std_h"><c>logger_std_h(3)</c></seealso>,
+        <seealso marker="sasl:sasl_app"><c>sasl(6)</c></seealso></p>
   </section>
 </chapter>
diff --git a/lib/kernel/doc/src/logger_disk_log_h.xml b/lib/kernel/doc/src/logger_disk_log_h.xml
index 440ae28e5d..20b49b8ca0 100644
--- a/lib/kernel/doc/src/logger_disk_log_h.xml
+++ b/lib/kernel/doc/src/logger_disk_log_h.xml
@@ -33,21 +33,21 @@
     <file>logger_disk_log_h.xml</file>
   </header>
   <module>logger_disk_log_h</module>
-  <modulesummary>A disk_log based handler for the Logger
-  application.</modulesummary>
+  <modulesummary>A disk_log based handler for the Logger.</modulesummary>
 
   <description>
-    <p>This is a handler for the Logger application that offers circular
-    (wrapped) logs by using the disk_log application. Multiple instances
-    of this handler can be added to logger, and each instance will print to
+    <p>This is a handler for Logger that offers circular
+    (wrapped) logs by using <seealso marker="disk_log"><c>disk_log</c></seealso>. 
+    Multiple instances
+    of this handler can be added to Logger, and each instance prints to
     its own disk_log file, created with the name and settings specified in
     the handler configuration.</p>
     <p>The default standard handler,
     <seealso marker="logger_std_h"><c>logger_std_h</c></seealso>, can be
-    replaced by a disk_log handler at startup of the kernel application.
+    replaced by a disk_log handler at startup of the Kernel application.
     See an example of this below.</p>
     <p>The handler has an overload protection mechanism that will keep the handler
-    process and the kernel application alive during a high load of log 
+    process and the Kernel application alive during a high load of log 
     requests. How this feature works, and how to modify the configuration,
     is described in the
     <seealso marker="logger_chapter#overload_protection"><c>User's Guide</c>
@@ -121,7 +121,7 @@ logger:add_handler(my_disk_log_h, logger_disk_log_h,
                               #{filesync_repeat_interval => 1000}}).
     </code>
     <p>In order to use the disk_log handler instead of the default standard
-    handler when starting en Erlang node, change the Kernel default logger to
+    handler when starting an Erlang node, change the Kernel default logger to
     use disk_log. Example:</p>
     <code type="none">
 erl -kernel logger '[{handler,default,logger_disk_log_h,
@@ -141,6 +141,12 @@ erl -kernel logger '[{handler,default,logger_disk_log_h,
 
   </funcs>
 
+  <section>
+    <title>See Also</title>
+    <p><seealso marker="logger"><c>logger(3)</c></seealso></p>
+    <p><seealso marker="logger_std_h"><c>logger_std_h(3)</c></seealso></p>
+    <p><seealso marker="disk_log"><c>disk_log(3)</c></seealso></p>
+  </section>
 </erlref>
 
 
diff --git a/lib/kernel/doc/src/logger_filters.xml b/lib/kernel/doc/src/logger_filters.xml
index 1bbae8be21..f92181ea3f 100644
--- a/lib/kernel/doc/src/logger_filters.xml
+++ b/lib/kernel/doc/src/logger_filters.xml
@@ -52,61 +52,100 @@
   <funcs>
     <func>
       <name name="domain" arity="2"/>
-      <fsummary>Filter log events based on the domain field in metadata.</fsummary>
+      <fsummary>Filter log events based on the domain field in
+	metadata.</fsummary>
       <desc>
-	  <p>This filter provides a way of filtering log events based on a
-	    <c>domain</c> field <c>Metadata</c>.</p>
-
-	  <p>The <c><anno>Extra</anno></c> parameter is specified when
-	    adding the filter
-	    via <seealso marker="logger#add_logger_filter-2">
-	      <c>logger:add_logger_filter/2</c></seealso>
-	    or <seealso marker="logger#add_handler_filter-3">
-	      <c>logger:add_handler_filter/3</c></seealso>.</p>
-
-	  <p>The filter compares the value of the <c>domain</c> field
-	    in the log event's metadata (<c>Domain</c>)
-	    to <c><anno>MatchDomain</anno></c> as follows:</p>
-
-	  <taglist>
-	    <tag><c><anno>Compare</anno> = starts_with</c></tag>
-	    <item><p>The filter matches if <c>MatchDomain</c> is a prefix
-	      of <c>Domain</c>.</p></item>
-	    <tag><c><anno>Compare</anno> = prefix_of</c></tag>
-	    <item><p>The filter matches if <c>Domain</c> is a prefix
-	      of <c>MatchDomain</c>.</p></item>
-	    <tag><c><anno>Compare</anno> = equals</c></tag>
-	    <item><p>The filter matches if <c>Domain</c> is equal
-	      to <c>MatchDomain</c>.</p></item>
-	    <tag><c><anno>Compare</anno> = differs</c></tag>
-	    <item><p>The filter matches if <c>Domain</c> differs
-	      from <c>MatchDomain</c>, or if there is no domain field
-	      in metadata.</p></item>
-	    <tag><c><anno>Compare</anno> = no_domain</c></tag>
-	    <item><p>The filter matches if there is no domain field in
-	      metadata. In this case <c><anno>MatchDomain</anno></c> shall
-	      be <c>[]</c>.</p></item>
-	  </taglist>
-
-          <p>If the filter matches and <c><anno>Action</anno> =
-            log</c>, the log event is allowed. If the filter matches
-            and <c><anno>Action</anno> = stop</c>, the log event is
-            stopped.</p>
-
-	  <p>If the filter does not match, it returns <c>ignore</c>,
-	    meaning that other filters, or the value of the
-	    configuration parameter <c>filter_default</c>, will decide
-	    if the event is allowed or not.</p>
-
-	  <p>Log events that do not contain any domain field, will
-	    only match when <c><anno>Compare</anno> = no_domain</c>.</p>
-
-	  <p>Example: stop all events with
-	    domain <c>[beam,erlang,otp,sasl|_]</c></p>
-
-	  <code>
+	<p>This filter provides a way of filtering log events based on a
+	  <c>domain</c> field in <c>Metadata</c>. This field is
+	  optional, and the purpose of using it is to group log events
+	  from, for example, a specific functional area. This allows
+	  filtering or other specialized treatment in a Logger
+	  handler.</p>
+
+	<p>A domain field must be a list of atoms, creating smaller
+	  and more specialized domains as the list grows longer. The
+	  biggest domain is <c>[]</c>, which comprices all
+	  possible domains.</p>
+
+	<p>For example, consider the following domains:</p>
+	<pre>
+D1 = [beam,erlang,otp]
+D2 = [beam,erlang,otp,sasl]</pre>
+
+	<p><c>D1</c> is the biggest of the two, and is said to be a
+	  super-domain of <c>D2</c>. <c>D2</c> is a
+	  sub-domain <c>D1</c>. Both <c>D1</c> and <c>D2</c> are
+	  sub-domains of <c>[]</c></p>
+
+	<p>The above domains are used for logs originating from
+	  Erlang/OTP. D1 specifies that the log event comes from
+	  Erlang/OTP in general, and D2 indicates that the log event
+	  is a so
+	  called <seealso marker="logger_chapter#sasl_reports">SASL
+	  report</seealso>.</p>
+
+	<p>The <c><anno>Extra</anno></c> parameter to
+	  the <c>domain/2</c> function is specified when adding the
+	  filter via <seealso marker="logger#add_logger_filter-2">
+	    <c>logger:add_logger_filter/2</c></seealso>
+	  or <seealso marker="logger#add_handler_filter-3">
+	    <c>logger:add_handler_filter/3</c></seealso>.</p>
+
+	<p>The filter compares the value of the <c>domain</c> field
+	  in the log event's metadata (<c>Domain</c>)
+	  to <c><anno>MatchDomain</anno></c> as follows:</p>
+
+	<taglist>
+	  <tag><c><anno>Compare</anno> = sub</c></tag>
+	  <item>
+	    <p>The filter matches if <c>Domain</c> is equal to or
+	      a sub-domain of <c>MatchDomain</c>, that is,
+	      if <c>MatchDomain</c> is a prefix of <c>Domain</c>.</p>
+	  </item>
+	  <tag><c><anno>Compare</anno> = super</c></tag>
+	  <item>
+	    <p>The filter matches if <c>Domain</c> is equal to or a
+	      super-domain of <c>MatchDomain</c>, that is,
+	      if <c>Domain</c> is a prefix of <c>MatchDomain</c>.</p>
+	  </item>
+	  <tag><c><anno>Compare</anno> = equal</c></tag>
+	  <item>
+	    <p>The filter matches if <c>Domain</c> is equal
+	      to <c>MatchDomain</c>.</p>
+	  </item>
+	  <tag><c><anno>Compare</anno> = not_equal</c></tag>
+	  <item>
+	    <p>The filter matches if <c>Domain</c> is not equal
+	      to <c>MatchDomain</c>, or if there is no domain field in
+	      metadata.</p>
+	  </item>
+	  <tag><c><anno>Compare</anno> = undefined</c></tag>
+	  <item><p>The filter matches if there is no domain field in
+	      metadata. In this case <c><anno>MatchDomain</anno></c>
+	      must be set to <c>[]</c>.</p>
+	  </item>
+	</taglist>
+
+        <p>If the filter matches and <c><anno>Action</anno> = log</c>,
+          the log event is allowed. If the filter matches
+          and <c><anno>Action</anno> = stop</c>, the log event is
+          stopped.</p>
+
+	<p>If the filter does not match, it returns <c>ignore</c>,
+	  meaning that other filters, or the value of the
+	  configuration parameter <c>filter_default</c>, decide if the
+	  event is allowed or not.</p>
+
+	<p>Log events that do not contain any domain field, match only
+	  when <c><anno>Compare</anno> = undefined</c>
+	  or <c><anno>Compare</anno> = not_equal</c>.</p>
+
+	<p>Example: stop all events with
+	  domain <c>[beam,erlang,otp,sasl|_]</c></p>
+
+	<code>
 logger:set_handler_config(h1,filter_default,log). % this is the default
-Filter = {fun logger_filters:domain/2,{stop,starts_with,[beam,erlang,otp,sasl]}}.
+Filter = {fun logger_filters:domain/2,{stop,sub,[beam,erlang,otp,sasl]}}.
 logger:add_handler_filter(h1,no_sasl,Filter).
 ok</code>
       </desc>
diff --git a/lib/kernel/doc/src/logger_formatter.xml b/lib/kernel/doc/src/logger_formatter.xml
index 370d61d338..02f89b26be 100644
--- a/lib/kernel/doc/src/logger_formatter.xml
+++ b/lib/kernel/doc/src/logger_formatter.xml
@@ -39,102 +39,157 @@
     <p>Each log handler has a configured formatter specified as a
       module and a configuration term. The purpose of the formatter is
       to translate the log events to a final printable string
-      (<c>unicode:chardata()</c>) which can be written to the output
+      (<seealso marker="stdlib:unicode#type-chardata"><c>unicode:chardata()</c>
+      </seealso>) which can be written to the output
       device of the handler.</p>
     <p><c>logger_formatter</c> is the default formatter used by
       Logger.</p>
   </description>
 
-  <section>
-    <title>Configuration</title>
-    <p>The configuration term for <c>logger_formatter</c> is a map,
-      and the following keys can be set as configuration
-      parameters:</p>
-    <taglist>
-      <tag><c>chars_limit = pos_integer() | unlimited</c></tag>
-      <item>
-	<p>A positive integer representing the value of the option
-	  with the same name to be used when calling
-	  <seealso marker="stdlib:io_lib#format-3">io_lib:format/3</seealso>.
-	  This value limits the total number of characters printed
-	  for each log event. Notice that this is a soft limit. For a
-	  hard truncation limit, see option <c>max_size</c>.</p>
-	<p>Default is <c>unlimited</c>.</p>
-	<note>
-	  <p><c>chars_limit</c> has no effect on log messages on
-	    string form. These are expected to be short, but can still
-	    be truncated by the <c>max_size</c> parameter.</p>
-	</note>
-      </item>
-      <tag><marker id="depth"/><c>depth = pos_integer() | unlimited</c></tag>
-      <item>
-	<p>A positive integer representing the maximum depth to
-	  which terms shall be printed by this formatter. Format
-	  strings passed to this formatter are rewritten. The format
-	  controls ~p and ~w are replaced with ~P and ~W,
-	  respectively, and the value is used as the depth
-	  parameter. For details, see
-	  <seealso marker="stdlib:io#format-2">io:format/2,3</seealso>
-	  in STDLIB.</p>
-	<p>Default is <c>unlimited</c>.</p>
-	<note>
-	  <p><c>depth</c> has no effect on log messages on string
-	    form. These are expected to be short, but can still be
-	    truncated by the <c>max_size</c> parameter.</p>
-	</note>
-      </item>
-      <tag><c>max_size = pos_integer() | unlimited</c></tag>
-      <item>
-	<p>A positive integer representing the absolute maximum size a
-	  string returned from this formatter can have. If the
-	  formatted string is longer, after possibly being limited
-	  by <c>chars_limit</c> or <c>depth</c>, it is truncated.</p>
-	<p>Default is <c>unlimited</c>.</p>
-      </item>
-      <tag><c>single_line = boolean()</c></tag>
-      <item>
-	<p>If set to <c>true</c>, all newlines in the message are
-	  replaced with <c>", "</c>, and whitespaces following
-	  directly after newlines are removed. Note that newlines
-	  added by the <c>template</c> parameter are not replaced.</p>
-	<p>Default is <c>true</c>.</p>
-      </item>
-      <tag><c>legacy_header = boolen()</c></tag>
-      <item>
-	<p>If set to <c>true</c> a header field is added to
-	  logger_formatter's part of <c>Metadata</c>. The value of
-	  this field is a string similar to the header created by the
-	  old <c>error_logger</c> event handlers. It can be included
-	  in the log event by adding the
-	  tuple <c>{logger_formatter,header}</c> to the template. See
-	  section <seealso marker="#default_templates">Default
-	  Templates</seealso> for more information.</p>
-	<p>Default is <c>false</c>.</p>
-      </item>
-      <tag><c>report_cb = fun((</c><seealso marker="logger#type-report"><c>logger:report()</c></seealso><c>) -> {</c><seealso marker="stdlib:io#type-format"><c>io:format()</c></seealso><c>,[term()]})</c></tag>
-      <item>
-	<p>A report callback is used by the formatter to transform log
-	  messages on report form to a format string and
-	  arguments. The report callback can be specified in the
-	  metadata for the log event. If no report callback exist in
-	  metadata, <c>logger_formatter</c> will
-	  use <seealso marker="logger#format_report-1">
-	    <c>logger:format_report/1</c></seealso> as default
-	  callback.</p>
-	<p>If this configuration parameter is set, it replaces both
-	  the default report callback, and any report callback found
-	  in metadata. That is, all reports are converted by this
-	  configured function.</p>
-	<p>The value must be a function with arity 1,
-	  returning <c>{Format,Args}</c>, and it will be called with a
-	  report as only argument.</p>
-      </item>
-      <tag><c>template = </c><seealso marker="#type-template"><c>template()</c></seealso></tag>
-      <item>
+
+  <datatypes>
+    <datatype>
+      <name name="config"/>
+      <desc>
+	<p>The configuration term for <c>logger_formatter</c> is a
+	  <seealso marker="stdlib:maps">map</seealso>, and the
+	  following keys can be set as configuration parameters:</p>
+	<taglist>
+	  <tag><c>chars_limit = pos_integer() | unlimited</c></tag>
+	  <item>
+	    <p>A positive integer representing the value of the option
+	      with the same name to be used when calling
+	      <seealso marker="stdlib:io_lib#format-3">
+		<c>io_lib:format/3</c></seealso>.
+	      This value limits the total number of characters printed
+	      for each log event. Notice that this is a soft limit. For a
+	      hard truncation limit, see option <c>max_size</c>.</p>
+	    <p>Defaults to <c>unlimited</c>.</p>
+	    <note>
+	      <p><c>chars_limit</c> has no effect on log messages on
+		string form. These are expected to be short, but can
+		still be truncated by the <c>max_size</c>
+		parameter.</p>
+	    </note>
+	  </item>
+	  <tag><marker id="depth"/><c>depth = pos_integer() | unlimited</c></tag>
+	  <item>
+	    <p>A positive integer representing the maximum depth to
+	      which terms shall be printed by this formatter. Format
+	      strings passed to this formatter are rewritten. The
+	      format controls ~p and ~w are replaced with ~P and ~W,
+	      respectively, and the value is used as the depth
+	      parameter. For details, see
+	      <seealso marker="stdlib:io#format-2">io:format/2,3</seealso>
+	      in STDLIB.</p>
+	    <p>Defaults to <c>unlimited</c>.</p>
+	    <note>
+	      <p><c>depth</c> has no effect on log messages on string
+		form. These are expected to be short, but can still be
+		truncated by the <c>max_size</c> parameter.</p>
+	    </note>
+	  </item>
+	  <tag><c>legacy_header = boolean()</c></tag>
+	  <item>
+	    <p>If set to <c>true</c> a header field is added to
+	      logger_formatter's part of <c>Metadata</c>. The value of
+	      this field is a string similar to the header created by
+	      the old <c>error_logger</c> event handlers. It can be
+	      included in the log event by adding the
+	      tuple <c>{logger_formatter,header}</c> to the
+	      template. See the description of
+	      the <seealso marker="#type-template"><c>template()</c></seealso>
+	      type for more information.</p>
+	    <p>Defaults to <c>false</c>.</p>
+	  </item>
+	  <tag><c>max_size = pos_integer() | unlimited</c></tag>
+	  <item>
+	    <p>A positive integer representing the absolute maximum size a
+	      string returned from this formatter can have. If the
+	      formatted string is longer, after possibly being limited
+	      by <c>chars_limit</c> or <c>depth</c>, it is truncated.</p>
+	    <p>Defaults to <c>unlimited</c>.</p>
+	  </item>
+	  <tag><c>report_cb = fun((</c><seealso marker="logger#type-report"><c>logger:report()</c></seealso><c>) -> {</c><seealso marker="stdlib:io#type-format"><c>io:format()</c></seealso><c>,[term()]})</c></tag>
+	  <item>
+	    <p>A report callback is used by the formatter to transform
+	      log messages on report form to a format string and
+	      arguments. The report callback can be specified in the
+	      metadata for the log event. If no report callback exist
+	      in metadata, <c>logger_formatter</c> will
+	      use <seealso marker="logger#format_report-1">
+		<c>logger:format_report/1</c></seealso> as default
+	      callback.</p>
+	    <p>If this configuration parameter is set, it replaces
+	      both the default report callback, and any report
+	      callback found in metadata. That is, all reports are
+	      converted by this configured function.</p>
+	    <p>The value must be a function with arity 1,
+	      returning <c>{Format,Args}</c>, and it will be called
+	      with a report as only argument.</p>
+	  </item>
+	  <tag><c>single_line = boolean()</c></tag>
+	  <item>
+	    <p>If set to <c>true</c>, all newlines in the message are
+	      replaced with <c>", "</c>, and whitespaces following
+	      directly after newlines are removed. Note that newlines
+	      added by the <c>template</c> parameter are not replaced.</p>
+	    <p>Defaults to <c>true</c>.</p>
+	  </item>
+	  <tag><c>template = </c><seealso marker="#type-template"><c>template()</c></seealso></tag>
+	  <item>
+	    <p>The template describes how the formatted string is
+	      composed by combining different data values from the log
+	      event. See the description of
+	      the <seealso marker="#type-template"><c>template()</c></seealso>
+	      type for more information about this.</p>
+	  </item>
+	  <tag><c>time_designator = byte()</c></tag>
+	  <item>
+	    <p>Timestamps are formatted according to RFC3339, and the
+	      time designator is the character used as date and time
+	      separator.</p>
+	    <p>Defaults to <c>$T</c>.</p>
+	    <p>The value of this parameter is used as
+	      the <c>time_designator</c> option
+	      to <seealso marker="stdlib:calendar#system_time_to_rfc3339-2">
+		<c>calendar:system_time_to_rcf3339/2</c></seealso>.</p>
+	  </item>
+	  <tag><c>time_offset = integer() | [byte()]</c></tag>
+	  <item>
+	    <p>The time offset, either a string or an integer, to be
+	      used when formatting the timestamp.</p>
+	    <p>An empty string is interpreted as local time. The
+	      values <c>"Z"</c>, <c>"z"</c> or <c>0</c> are
+	      interpreted as Universal Coordinated Time (UTC).</p>
+	    <p>Strings, other than <c>"Z"</c>, <c>"z"</c>,
+	      or <c>""</c>, must be on the form <c>±[hh]:[mm]</c>, for
+	      example <c>"-02:00"</c> or <c>"+00:00"</c>.</p>
+	    <p>Integers must be in microseconds, meaning that the
+	      offset <c>7200000000</c> is equivalent
+	      to <c>"+02:00"</c>.</p>
+	    <p>Defaults to an empty string, meaning that timestamps
+	      are displayed in local time. However, for backwards
+	      compatibility, if the SASL configuration
+	      parameter <seealso marker="sasl:sasl_app#utc_log">
+		<c>utc_log</c></seealso><c>=true</c>, the default is
+	      changed to <c>"Z"</c>, meaning that timestamps are displayed
+	      in UTC.</p>
+	    <p>The value of this parameter is used as
+	      the <c>offset</c> option
+	      to <seealso marker="stdlib:calendar#system_time_to_rfc3339-2">
+		<c>calendar:system_time_to_rcf3339/2</c></seealso>.</p>
+	  </item>
+	</taglist>
+      </desc>
+    </datatype>
+    <datatype>
+      <name name="template"/>
+      <desc>
 	<p>The template is a list of atoms, tuples and strings. The
 	  atoms <c>level</c> or <c>msg</c>, are treated as
 	  placeholders for the severity level and the log message,
-	  repectively. Other atoms or tuples are interpreted as
+	  respectively. Other atoms or tuples are interpreted as
 	  placeholders for metadata, where atoms are expected to match
 	  top level keys, and tuples represent paths to sub keys when
 	  the metadata is a nested map. For example the
@@ -152,107 +207,85 @@
         <p>Strings in the template are printed literally.</p>
 	<p>The default template differs depending on the values
 	  of <c>legacy_header</c>
-	  and <c>single_line</c>. See <seealso marker="#default_templates">Default
-	  Templates</seealso> for more information</p>
-      </item>
-      <tag><c>time_designator = byte()</c></tag>
-      <item>
-	<p>Timestamps are formatted according to RFC3339, and the time
-	  designator is the character used as date and time
-	  separator.</p>
-	<p>Default is <c>$T</c>.</p>
-	<p>The value of this parameter is used as
-	  the <c>time_designator</c> option
-	  to <seealso marker="stdlib:calendar#system_time_to_rfc3339-2">
-	    <c>calendar:system_time_to_rcf3339/2</c></seealso>.</p>
-      </item>
-      <tag><c>time_offset = integer() | [byte()]</c></tag>
-      <item>
-	<p>The time offset, either a string or an integer, to be
-	  used when formatting the timestamp.</p>
-	<p>An empty string is interpreted as local time. The
-	  values <c>"Z"</c>, <c>"z"</c> or <c>0</c> are interpreted as
-	  Universal Coordinated Time (UTC).</p>
-	<p>Strings, other than <c>"Z"</c>, <c>"z"</c>, or <c>""</c>,
-	  must be on the form <c>±[hh]:[mm]</c>, for
-	  example <c>"-02:00"</c> or <c>"+00:00"</c>.</p>
-	<p>Integers must be in microseconds, meaning that the
-	  offset <c>7200000000</c> is equivalent
-	  to <c>"+02:00"</c>.</p>
-	<p>The default value is an empty string, meaning that
-	  timestamps are displayed in local time. However, for
-	  backwards compatibility, if the SASL environment
-	  variable <seealso marker="sasl:sasl_app#utc_log">
-	    <c>utc_log</c></seealso><c>=true</c>, the default is
-	  changed to <c>"Z"</c>, meaning that timestamps are displayed
-	  in UTC.</p>
-	<p>The value of this parameter is used as the <c>offset</c>
-	  option to <seealso marker="stdlib:calendar#system_time_to_rfc3339-2">
-	    <c>calendar:system_time_to_rcf3339/2</c></seealso>.</p>
-      </item>
-    </taglist>
-  </section>
+	  and <c>single_line</c>:</p>
 
-  <section>
-    <marker id="default_templates"/>
-    <title>Default templates</title>
+	<p>The default value for the <c>template</c> configuration
+	  parameter depends on the value of the <c>single_line</c>
+	  and <c>legacy_header</c> configuration parameters as
+	  follows.</p>
 
-    <p>The default value for the <c>template</c> configuration
-      parameter depends on the value of <c>single_line</c>
-      and <c>legacy_header</c> as follows.</p>
-
-    <p>The log event used in the examples is:</p>
-    <code>
+	<p>The log event used in the examples is:</p>
+	<code>
 ?LOG_ERROR("name: ~p~nexit_reason: ~p",[my_name,"It crashed"])</code>
 
-    <taglist>
-      <tag><c>legacy_header=true</c></tag>
-      <item>
-	<p>Default template: <c>[{logger_formatter,header},"\n",msg,"\n"]</c></p>
+	<taglist>
+	  <tag><c>legacy_header=true, single_line=false</c></tag>
+	  <item>
+	    <p>Default
+	    template: <c>[{logger_formatter,header},"\n",msg,"\n"]</c></p>
 
-	<p>Example log entry:</p>
-	<code type="none">
-2018-05-16T11:55:50.448382+02:00 error:
+	    <p>Example log entry:</p>
+	    <code type="none">
+=ERROR REPORT==== 17-May-2018::18:30:19.453447 ===
 name: my_name
 exit_reason: "It crashed"</code>
 
-	<p>Notice that all eight levels might occur in the heading,
-	  not only <c>ERROR</c>, <c>WARNING</c> or <c>INFO</c> as the
-	  old <c>error_logger</c> produced. And microseconds are
-	  added at the end of the timestamp.</p>
-      </item>
+	    <p>Notice that all eight levels can occur in the heading,
+	      not only <c>ERROR</c>, <c>WARNING</c> or <c>INFO</c> as the
+	      old <c>error_logger</c> produced. And microseconds are
+	      added at the end of the timestamp.</p>
+	  </item>
+
+	  <tag><c>legacy_header=true, single_line=true</c></tag>
+	  <item>
+	    <p>Default
+	    template: <c>[{logger_formatter,header},"\n",msg,"\n"]</c></p>
 
-      <tag><c>single_line=true</c></tag>
-      <item>
-	<p>Default template: <c>[time," ",level,": ",msg,"\n"]</c></p>
+	    <p>Notice that the template is here the same as
+	      for <c>single_line=false</c>, but the resulting log entry
+	      differs in that there is only one line after the
+	      heading:</p>
+	    <code type="none">
+=ERROR REPORT==== 17-May-2018::18:31:06.952665 ===
+name: my_name, exit_reason: "It crashed"</code>
+	  </item>
 
-	<p>Example log entry:</p>
-	<code type="none">2018-05-16T11:55:50.448382+02:00 error: name: my_name, exit_reason: "It crashed"</code>
-      </item>
+	  <tag><c>legacy_header=false, single_line=true</c></tag>
+	  <item>
+	    <p>Default template: <c>[time," ",level,": ",msg,"\n"]</c></p>
 
-      <tag><c>legacy_header=false, single_line=false</c></tag>
-      <item>
-	<p>Default template: <c>[time," ",level,":\n",msg,"\n"]</c></p>
+	    <p>Example log entry:</p>
+	    <code type="none">
+2018-05-17T18:31:31.152864+02:00 error: name: my_name, exit_reason: "It crashed"</code>
+	  </item>
 
-	<p>Example log entry:</p>
-	<code type="none">
-2018-05-16T11:55:50.448382+02:00 error:
+	  <tag><c>legacy_header=false, single_line=false</c></tag>
+	  <item>
+	    <p>Default template: <c>[time," ",level,":\n",msg,"\n"]</c></p>
+
+	    <p>Example log entry:</p>
+	    <code type="none">
+2018-05-17T18:32:20.105422+02:00 error:
 name: my_name
 exit_reason: "It crashed"</code>
-      </item>
-    </taglist>
-  </section>
-
-  <datatypes>
-    <datatype>
-      <name name="template"/>
-      <desc>
+	  </item>
+	</taglist>
       </desc>
     </datatype>
   </datatypes>
 
   <funcs>
     <func>
+      <name name="check_config" arity="1"/>
+      <fsummary>Validates the given formatter configuration.</fsummary>
+      <desc>
+	<p>This callback function is called by Logger when the
+	  formatter configuration for a handler is set or modified. It
+	  returns <c>ok</c> if the configuration is valid,
+	  and <c>{error,term()}</c> if it is faulty.</p>
+      </desc>
+    </func>
+    <func>
       <name name="format" arity="2"/>
       <fsummary>Formats the given message.</fsummary>
       <desc>
@@ -274,7 +307,6 @@ exit_reason: "It crashed"</code>
 	</list>
       </desc>
     </func>
-
   </funcs>
 
 </erlref>
diff --git a/lib/kernel/doc/src/logger_std_h.xml b/lib/kernel/doc/src/logger_std_h.xml
index bf23d874c8..a4f2848037 100644
--- a/lib/kernel/doc/src/logger_std_h.xml
+++ b/lib/kernel/doc/src/logger_std_h.xml
@@ -33,17 +33,17 @@
     <file>logger_std_h.xml</file>
   </header>
   <module>logger_std_h</module>
-  <modulesummary>Default handler for the Logger application.</modulesummary>
+  <modulesummary>Default handler for Logger.</modulesummary>
 
   <description>
-    <p>This is the default handler for the Logger
-      application. Multiple instances of this handler can be added to
-      logger, and each instance will print logs to <c>standard_io</c>,
+    <p>This is the default handler for Logger.
+      Multiple instances of this handler can be added to
+      Logger, and each instance will print logs to <c>standard_io</c>,
       <c>standard_error</c> or to file. The default instance that starts
-      with kernel is named <c>default</c> - which is the name to be used
+      with Kernel is named <c>default</c> - which is the name to be used
       for reconfiguration.</p>
     <p>The handler has an overload protection mechanism that will keep the handler
-      process and the kernel application alive during a high load of log 
+      process and the Kernel application alive during a high load of log 
       requests. How this feature works, and how to modify the configuration,
       is described in the
       <seealso marker="logger_chapter#overload_protection"><c>User's Guide</c>
@@ -104,7 +104,7 @@ logger:add_handler(my_standard_h, logger_std_h,
                                 filesync_repeat_interval => 1000}}).
     </code>
     <p>In order to configure the default handler (that starts initially with
-    the kernel application) to log to file instead of <c>standard_io</c>,
+    the Kernel application) to log to file instead of <c>standard_io</c>,
     change the Kernel default logger to use a file. Example:</p>
     <code type="none">
 erl -kernel logger '[{handler,default,logger_std_h,
@@ -127,6 +127,11 @@ erl -kernel logger '[{handler,default,logger_std_h,
 
   </funcs>
 
+  <section>
+    <title>See Also</title>
+    <p><seealso marker="logger"><c>logger(3)</c></seealso></p>
+    <p><seealso marker="logger_disk_log_h"><c>logger_disk_log_h(3)</c></seealso></p>
+  </section>
 </erlref>