man: clarify criteria (incl. PCRE2 usage)

Replace the XWayland-only class attribute in the examples:
- The first example given should work for Wayland-native windows.
- The example 'Kill all windows with the title "Emacs"' should use
  title, not class. Also, it's a substring (regex) match.

There are many different implementations of regular expressions with
incompatible syntax. For example, GNU grep alone provides three
different ones. Clarify the use of PCRE2 by sway criteria.

sway/sway.5.scd

@@ -972,7 +972,7 @@ The default colors are:
 A criteria is a string in the form of, for example:
 
 ```
-[class="[Rr]egex.*" title="some title"]
+[app_id="some-application" title="[Rr]egex.*"]
 ```
 
 The string contains one or more (space separated) attribute/value pairs. They
@@ -992,10 +992,19 @@ Focus on a window with the mark "IRC":
 [con_mark="IRC"] focus
 ```
 
-Kill all windows with the title "Emacs":
+Kill all windows where the title contains "Emacs":
 
 ```
-[class="Emacs"] kill
+[title="Emacs"] kill
+```
+
+Several attributes allow regular expressions. These use Perl-compatible regular
+expressions (PCRE2), which are documented in *pcre2pattern*(3) and summarized in
+*pcre2syntax*(3). For example, this moves all windows with titles ending in
+"sway" or "Sway" to workspace 1:
+
+```
+[title="[Ss]way$"] move workspace 1
 ```
 
 You may like to use swaymsg -t get_tree for finding the values of these
@@ -1094,3 +1103,4 @@ The following attributes may be matched with:
 # SEE ALSO
 
 *sway*(1) *sway-input*(5) *sway-output*(5) *sway-bar*(5) *sway-ipc*(7)
+*pcre2pattern*(3) *pcre2syntax*(3)