Add a section about named regexes

Author: Mouq

lib/Language/grammars.pod

@@ -14,14 +14,38 @@ L<JSON::Simple module|https://github.com/moritz/json>, which can
 deserialize any valid JSON file, and yet the deserializing code is
 written in less than 100 lines of simple, extensible code.
 
+=head1 Named Regexes
+
+The main ingredients of grammars are named L<regexes|/language/regexes>.
+These have a special syntax, similar to subroutine definitions:
+
+=for code :allow<B>
+my B<regex number {> \d+ [ \. \d+ ]? B<}>
+
+In this case, we have to specify that the regex is lexically scoped
+using the C<my> keyword, because named regexes are normally used within
+grammars.
+
+Being named gives us the advantage of being able to easily reuse the
+regex elsewhere:
+
+    =begin code :allow<B>
+    say "32.51" ~~ B<&number>;
+    say "15 + 4.5" ~~ /B<< <number> >>\s* '+' \s*B<< <number> >>/
+    =end code
+
+TODO signatures
+
+TODO tokens & rules
+
 =head1 class Grammar
 
     class Grammar is Cursor { }
 
 C<Grammar> is the superclass that classes automatically get when they
 are declared with the C<grammar> keyword instead of C<class>. Grammars
 should only be used to parse text; if you wish to extract complex data,
-an L<action class|/language/grammars#Action classes> is recommended to
+an L<action class|/language/grammars#Action_Classes> is recommended to
 be used in conjunction with the grammar.
 
     =begin code :allow<B L>
@@ -117,7 +141,7 @@ of the supplied string.
 Parses the contents of the file C<$filename> with the L<parse> method,
 passing along any named options in C<%opts>.
 
-=head1 Action classes
+=head1 Action Classes
 
 TODO