It seems to be against several goals of Creole. There is already a markup similar to this proposal, less verbose, with end tags which can be recognized easily, standard and very popular: XML. Since Creole doesn't use single angle brackets, it would be easy to mix both.
We're soon going to have assigned a meaning to all double punctuation signs, so Creole won't be much more complicated than it is now. I'd suggest to reserve $$ for LaTeX math, __ for underlined, -- for deleted text and ++ and %% for future uses (all optional), and we're done. Both !! and ?? are too frequent in plain text to be safe.
-- YvesPiguet, 2007-Apr-2
As far as I know, XML is a general markup language, not a set of text formatting rules. You surely mean HTML or XHMTL or one of the other text-formatting SGML/XML derivatives :)
I'd say that "--" is also too frequent in text to use it for markup, so while it fits so fine semantically with "deleted" and visually with "strike trough", it is better avoided -- see the discussions in HyphenListMarkupProposal. You can always use things like "[-foo-]" of course, but we are just making a poor reimplementation of HTML and friends this way.
-- Radomir Dopieralski, 2007-Apr-03
XML: yes, anything more or less based on SGML, XML or SML
would be better than underscores, and this should be left outside Creole Core.
Double hyphens: I thought the same quickly after posting, but I didn't want to hide my point with a minor edit.
-- YvesPiguet, 2007-Apr-03