It started by yours truly asking impertinent questions on #perl6... <http://irclog.perlgeek.de/perl6/2009-03-26#i_1018345>
...and ended with a general feeling that the way metacharacters and backwhacking work in <[ ]> character classes, is at worst inconsistent and at best underspecified by S05. Specifically, the following paragraphs from that spec do _not_ hold for character classes, which are more like a sublanguage of their own: ] Unlike traditional regular expressions, Perl 6 does not require ] you to memorize an arbitrary list of metacharacters. Instead it ] classifies characters by a simple rule. All glyphs (graphemes) ] whose base characters are either the underscore (C<_>) or have ] a Unicode classification beginning with 'L' (i.e. letters) or 'N' ] (i.e. numbers) are always literal (i.e. self-matching) in regexes. They ] must be escaped with a C<\> to make them metasyntactic (in which ] case that single alphanumeric character is itself metasyntactic, ] but any immediately following alphanumeric character is not). ] ] All other glyphs--including whitespace--are exactly the opposite: ] they are always considered metasyntactic (i.e. non-self-matching) and ] must be escaped or quoted to make them literal. As is traditional, ] they may be individually escaped with C<\>, but in Perl 6 they may ] be also quoted as follows. In character classes, most 'other glyphs' mean themselves, just like alphanumerics, with a few notable exceptions: backslash (\), closing bracket (]) and dash (-) and whitespace still need to be backwhacked. All other characters are treated literally, including dot (.) which is actually used for metasyntactic purposes in character classes. In other words, currently /<[.]>/ is legal, but /<[-]>/ is not. Which is kinda weird, if you ask me. See the linked #perl6 log for details. What's the big-picture rule of thumb regarding metacharacters in character classes? // Carl
