matchparen: do not use hard-coded match id (#13393)

* matchparen: do not use hard-coded match id

Instead of using the hard-coded match id 3, which may also be used by
other plugins, let the matchparen plugin use whatever ids are
automatically returned when calling matchaddpos().

For backwards-compatibility, keep the `:3match` call, which will still
use the hard-coded id 3 (as mentioned in :h :3match).

closes: #13381

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/pattern.txt b/runtime/doc/pattern.txt
index 4fa26e0..983d995 100644
--- a/runtime/doc/pattern.txt
+++ b/runtime/doc/pattern.txt
@@ -1,4 +1,4 @@
-*pattern.txt*   For Vim version 9.0.  Last change: 2023 Feb 04
+*pattern.txt*   For Vim version 9.0.  Last change: 2023 Oct 20
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -1461,10 +1461,11 @@
 		Just like |:match| above, but set a separate match.  Thus
 		there can be three matches active at the same time.  The match
 		with the lowest number has priority if several match at the
-		same position.
-		The ":3match" command is used by the |matchparen| plugin.  You
-		are suggested to use ":match" for manual matching and
-		":2match" for another plugin.
+		same position.  It uses the match id 3.
+		The ":3match" command is used by (older Vims) |matchparen|
+		plugin. You are suggested to use ":match" for manual matching
+		and ":2match" for another plugin or even better make use of
+		the more flexible |matchadd()| (and similar) functions instead.
 
 ==============================================================================
 11. Fuzzy matching					*fuzzy-matching*