If the function wants to handle the keyword, it first must
parse anything following the keyword that is part of the syntax
-introduced by the keyword. The lexer interface is poorly documented.
-Broadly speaking, parsing needs to look at the buffer that extends
-from C<PL_parser-E<gt>bufptr> to C<PL_parser-E<gt>bufend>, and
-C<PL_parser-E<gt>bufptr> must be advanced across whatever text is
-consumed by the parsing process. The buffer end is not necessarily the
-real end of the input text, but refilling the buffer is too complicated
-to discuss here. See L<Devel::Declare> for some parsing experience,
-and hope for more core support in a future version of Perl.
+introduced by the keyword. See L</Lexer interface> for details.
When a keyword is being handled, the plugin function must build
a tree of C<OP> structures, representing the code that was parsed.