Put here all your craziest ideas about syntax highlighting features which are needed but missing (but only those which don't require changing lang files format in an incompatible way, that can wait for another ten years, to be in gtksourceview-3). I expect stuff here to be actually implemented. But we need to decide what's needed, what's badly needed, and what can wait till next century.

• Sane child context ordering/matching: make it possible to specify that context A must be first, context C may come only after context B, context D may match only once, etc.

• Skip beginnings of lines when using some context. For example, gtk-doc comments (and alike): they are C comments, with content which could be highlighted, but usually every line has characters which aren't proper part of that highlighted content, like

  /**
   * Some xml <here
   * continues="true"/> but the asterisks should
   * be ignored
   */

  It's possible to ask for more here, namely to ask to highlight some arbitrary subregions of text, but this smaller one is at least possible to implement (or so it seems). In particular, nud's one about matching a piece and then applying highlighting to that piece is a different thing.
• Define some non-code standard markup types (you known the 'comment', 'keyword' etc), for _markup_ languages, that are also used with gtksourceview (for example latex, markdown and wikitext). Such standard formattings are for example "emphasis" and "headline", more can be invented.
  • Please do invent those, make up a nice list of those styles and post it in bugzilla (the bug report says same thing, "emphasis etc."). What's "headline" anyway? Note that syntax highlighting will not change font (it could, but it'd be a separate feature). - muntyan