Clarifying "lookaround" assertions according ot answers in rakudo/rak…

…udo#3800

Checking item in #2632

doc/Language/regexes.pod6

@@ -1295,16 +1295,21 @@ C<bar> would match with
 
     say "foobaz" ~~ / foo <!before bar> /;  # OUTPUT: «foo␤»
 
-Lookahead assertions can be used also with other patterns, like
-characters ranges, interpolated variables, subscripts and so on. In such
-cases it does suffice to use a C<?>, or a C<!> for the negate form.
-For instance, the following lines all produce the very same result:
+Lookahead assertions can be used also with other patterns, like characters
+ranges, interpolated variables subscripts and so on. In such cases it does
+suffice to use a C<?>, or a C<!> for the negate form. For instance, the
+following lines all produce the very same result:
 
     say 'abcdefg' ~~ rx{ abc <?before def> };        # OUTPUT: «｢abc｣␤»
     say 'abcdefg' ~~ rx{ abc <?[ d..f ]> };          # OUTPUT: «｢abc｣␤»
     my @ending_letters = <d e f>;
     say 'abcdefg' ~~ rx{ abc <?@ending_letters> };   # OUTPUT: «｢abc｣␤»
 
+Metacharacters can also be used in lookahead or -behind assertions.
+
+    say "First. Second" ~~ m:g/ <?after ^^ | "." \s+> <:Lu>\S+ /
+    # OUTPUT: «(｢First.｣ ｢Second｣)␤»
+
 A practical use of lookahead assertions is in substitutions, where
 you only want to substitute regex matches that are in a certain
 context. For example, you might want to substitute only numbers