Clarify option errors in the manual for gun:open/open_unix

Also fix an http into http2 for one option.

2 files changed, 9 insertions, 5 deletions

diff --git a/doc/src/manual/gun.open.asciidoc b/doc/src/manual/gun.open.asciidoc
index 2e6c8b9..79a9d54 100644
--- a/doc/src/manual/gun.open.asciidoc
+++ b/doc/src/manual/gun.open.asciidoc
@@ -9,11 +9,13 @@ gun:open - Open a connection to the given host and port
 [source,erlang]
 ----
 open(Host, Port)       -> open(Host, Port, #{})
-open(Host, Port, Opts) -> {ok, pid()} | {error, any()}
+open(Host, Port, Opts) -> {ok, pid()} | {error, Reason}
 
-Host :: inet:hostname() | inet:ip_address()
-Port :: inet:port_number()
-Opts :: gun:opts()
+Host    :: inet:hostname() | inet:ip_address()
+Port    :: inet:port_number()
+Opts    :: gun:opts()
+Reason  :: {options, OptName} | {options, {http | http2, OptName}} | any()
+OptName :: atom()
 ----
 
 Open a connection to the given host and port.
diff --git a/doc/src/manual/gun.open_unix.asciidoc b/doc/src/manual/gun.open_unix.asciidoc
index 225ecc8..4ea8d2b 100644
--- a/doc/src/manual/gun.open_unix.asciidoc
+++ b/doc/src/manual/gun.open_unix.asciidoc
@@ -8,10 +8,12 @@ gun:open_unix - Open a connection to the given Unix domain socket
 
 [source,erlang]
 ----
-open_unix(SocketPath, Opts) -> {ok, pid()} | {error, any()}
+open_unix(SocketPath, Opts) -> {ok, pid()} | {error, Reason}
 
 SocketPath :: string()
 Opts       :: gun:opts()
+Reason     :: {options, OptName} | {options, {http | http2, OptName}} | any()
+OptName    :: atom()
 ----
 
 Open a connection to the given Unix domain socket.