Did you already get in contact with the Scintilla team as beside the issue your Lexxer would be also a nice one to be included into Scintilla itself.

not yet, because it's easier for me to recompile Geany rather than to use Scintilla and Scite. But I'll do it soon I think.

I've updated the lexer and now it's almost fully fonctional. Now for symbol such as -- which is not correcty terminated (it could be written like this, for example if the author is refering to a command line switch), it won't last beyond the end of the current line, but I'd prefer it to begin to color the text only if there are both symbols around it (like for the URL).

Here is a screenshot: http://img641.imageshack.us/img641/2791/geanytxt2tagslexer.png