Rephrases sentence, closes #2409

Author: JJ

doc/Language/regexes.pod6

@@ -1578,9 +1578,10 @@ 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: 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.
+The so-called I<regex> adverbs apply at the point where a regex is defined;
+additionally, I<matching> adverbs apply at the point that a regex matches
+against a string and I<substitution> adverbs are applied exclusively in
+substitutions.
 
 This distinction often blurs, because matching and declaration are often
 textually close but using the method form of matching, that is, C<.match>, makes