Adds clarification for non-collating two-letter adverbs

Which closes #2406. Also some reflow and rephrasing.

Author: JJ

doc/Language/regexes.pod6

@@ -1573,16 +1573,17 @@ say $/<ipv4-octet>;   # OUTPUT: [｢127｣ ｢0｣ ｢0｣ ｢1｣]
 
 =head1 Adverbs
 
-Adverbs modify how regexes work and provide convenient shortcuts for
-certain kinds of recurring tasks.
+Adverbs, which modify how regexes work and provide convenient shortcuts for
+certain kinds of recurring tasks, are combinations of one or more letters
+preceded by a colon C<:>.
 
-There are two kinds of adverbs: regex adverbs apply at the point where a
-regex is defined and matching adverbs apply at the point that a regex
+There are two kinds of adverbs: I<regex> adverbs apply at the point where a
+regex is defined, and I<matching> adverbs apply at the point that a regex
 matches against a string.
 
 This distinction often blurs, because matching and declaration are often
-textually close but using the method form of matching makes the distinction
-clear.
+textually close but using the method form of matching, that is, C<.match>, makes
+the distinction clear.
 
 C<'abc' ~~ /../> is roughly equivalent to C<'abc'.match(/../)>, or even more
 clearly written in separate lines:
@@ -1592,8 +1593,8 @@ clearly written in separate lines:
         say "'abc' has at least two characters";
     }
 
-Regex adverbs like C<:i> go into the definition line and matching adverbs
-like C<:overlap> are appended to the match call:
+Regex adverbs like C<:i> go into the definition line and matching adverbs like
+C<:overlap> (which can be abbreviated to C<:ov>) are appended to the match call:
 
     my $regex = /:i . a/;
     for 'baA'.match($regex, :overlap) -> $m {
@@ -1603,7 +1604,7 @@ like C<:overlap> are appended to the match call:
 
 =head2 X<Regex adverbs|regex adverb,:ignorecase;regex adverb,:i>
 
-Adverbs that appear at the time of a regex declaration are part of the
+The adverbs that appear at the time of a regex declaration are part of the
 actual regex and influence how the Perl 6 compiler translates the regex into
 binary code.
 
@@ -1612,15 +1613,14 @@ the distinction between upper case, lower case and title case letters.
 
 So C<'a' ~~ /A/> is false, but C<'a' ~~ /:i A/> is a successful match.
 
-Regex adverbs can come before or inside a regex declaration and only affect
-the part of the regex that comes afterwards, lexically.
-Note that regex adverbs appearing before the regex must appear after
-something that introduces the regex to the parser, like 'rx' or 'm' or a bare '/'.
-This is NOT valid:
+Regex adverbs can come before or inside a regex declaration and only affect the
+part of the regex that comes afterwards, lexically. Note that regex adverbs
+appearing before the regex must appear after something that introduces the regex
+to the parser, like 'rx' or 'm' or a bare '/'. This is NOT valid:
 
-    =begin code :skip-test
-    my $rx1 = :i/a/;      # adverb is before the regex is recognized => exception
-    =end code
+=begin code :skip-test
+my $rx1 = :i/a/;      # adverb is before the regex is recognized => exception
+=end code
 
 but these are valid:
 
@@ -1643,6 +1643,13 @@ Square brackets and parentheses limit the scope of an adverb:
     / (:i a b) c /;         # matches 'ABc' but not 'ABC'
     / [:i a b] c /;         # matches 'ABc' but not 'ABC'
 
+When two adverbs are used together, they keep their colon at the front
+
+    "þor is Þor" ~~ m:g:i/þ/;# OUTPUT: «(｢þ｣ ｢Þ｣)␤»
+
+That implies that when there are two vowels together after a C<:>, they
+correspond to the same adverb, as in C<:ov> or C<:P5>.
+
 =head3 X<Ignoremark|regex adverb,:ignoremark;regex adverb,:m>
 
 The C<:ignoremark> or C<:m> adverb instructs the regex engine to only