These are directives that change how DWikiText is interpreted to do things like turn off certain font characters or map a simple-to-type character sequence like '->' to a HTML entity. They are documented in DWikiText so I am not going to repeat myself here.
In the process I added a new and less annoying plain quoting mechanism: ``...''. It looks better in ASCII than it probably does in the font here.
(The code for this was written in August of 2007 or so, but I sat on it because I wasn't entirely sure I liked the feature. Well, nuts to that; time to roll things out and just go.)