Add token/rule explaination to grammars.pod

lib/Language/grammars.pod

@@ -16,8 +16,11 @@ 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:
+The main ingredient of grammars is named L<regexes|/language/regexes>.  While
+the syntax of L<Perl 6 Regexes|/language/regexes> is outside the scope of this
+document, I<named> regexes have a special syntax, similar to subroutine
+definitions:N<In fact, named regexes can even take extra arguments, using the
+same syntax as subroutine parameter lists>
 
 =for code :allow<B>
 my B<regex number {> \d+ [ \. \d+ ]? B<}>
@@ -34,9 +37,29 @@ regex elsewhere:
     say "15 + 4.5" ~~ /B<< <number> >>\s* '+' \s*B<< <number> >>/
     =end code
 
-TODO signatures
+B<C<regex>> isn't the only declarator for named regexes -- in fact, it's the
+least common. Most of the time, the B<C<token>> or B<C<rule>> declarators are
+used. These are both I<ratcheting>, which means that the match engine won't
+back up and try again if it fails to match something. This will usually do what you want, but isn't appropriate for all cases:
 
-TODO tokens & rules
+    =begin code :allow<B>
+    my regex works-but-slow { .+ q }
+    my token fails-but-fast { .+ q }
+    my $s = 'Tokens won't backtrack, which makes them fail quicker!';
+    say so $s ~~ &works-but-slow; # True
+    say so $s ~~ &fails-but-fast; # False, the entire string get taken by the .+
+    =end code
+
+The only difference between the C<token> and C<rule> declarators is that the
+C<rule> declarator causes L<C<:sigspace>|/language/regexes#sigspace> to go into
+effect for the Regex:
+
+    =begin code :allow<B>
+    my token non-space-y { once upon a time }
+    my rule space-y { once upon a time }
+    say 'onceuponatime'    ~~ &non-space-y;
+    say 'once upon a time' ~~ &space-y;
+    =end code
 
 =head1 class Grammar