DOC: management: Clearly state "show errors" only reports malformed H1 messages

For now, only the H1 multiplexer is able to capture malformed messages. So
it is better to update the management guide accordingly to avoid any
confusion.

Author: capflam

doc/management.txt

@@ -2820,14 +2820,14 @@ show env [<name>]
   can only be issued on sockets configured for levels "operator" or "admin".
 
 show errors [<iid>|<proxy>] [request|response]
-  Dump last known request and response errors collected by frontends and
-  backends. If <iid> is specified, the limit the dump to errors concerning
-  either frontend or backend whose ID is <iid>. Proxy ID "-1" will cause
-  all instances to be dumped. If a proxy name is specified instead, its ID
-  will be used as the filter. If "request" or "response" is added after the
-  proxy name or ID, only request or response errors will be dumped. This
-  command is restricted and can only be issued on sockets configured for
-  levels "operator" or "admin".
+  Dump last known HTTP/1.x request and response errors collected by frontends
+  and backends. If <iid> is specified, the limit the dump to errors concerning
+  either frontend or backend whose ID is <iid>. Proxy ID "-1" will cause all
+  instances to be dumped. If a proxy name is specified instead, its ID will be
+  used as the filter. If "request" or "response" is added after the proxy name
+  or ID, only request or response errors will be dumped. This command is
+  restricted and can only be issued on sockets configured for levels "operator"
+  or "admin".
 
   The errors which may be collected are the last request and response errors
   caused by protocol violations, often due to invalid characters in header
@@ -4537,17 +4537,17 @@ connections are handled in parallel, though the "debug2ansi" and "debug2html"
 scripts found in the examples/ directory definitely help here by coloring the
 output.
 
-If a request or response is rejected because HAProxy finds it is malformed, the
-best thing to do is to connect to the CLI and issue "show errors", which will
-report the last captured faulty request and response for each frontend and
-backend, with all the necessary information to indicate precisely the first
-character of the input stream that was rejected. This is sometimes needed to
-prove to customers or to developers that a bug is present in their code. In this
-case it is often possible to relax the checks (but still keep the captures)
-using "option accept-unsafe-violations-in-http-request" or its equivalent for
-responses coming from the server "option
-accept-unsafe-violations-in-http-response". Please see the configuration manual
-for more details.
+If a HTTP/1.x request or response is rejected because HAProxy finds it is
+malformed, the best thing to do is to connect to the CLI and issue "show
+errors", which will report the last captured faulty HTTP/1.x request and
+response for each frontend and backend, with all the necessary information to
+indicate precisely the first character of the input stream that was
+rejected. This is sometimes needed to prove to customers or to developers that a
+bug is present in their code. In this case it is often possible to relax the
+checks (but still keep the captures) using "option
+accept-unsafe-violations-in-http-request" or its equivalent for responses coming
+from the server "option accept-unsafe-violations-in-http-response". Please see
+the configuration manual for more details.
 
 Example :