Syntax highlighting spans where the end condition depends on the begin condition

[khhelland]

Hi, I'm using AvalonEdit for a Lua editor. I want to properly highlight multiline comments, but the end condition can depend on the begining condition.
The format is
"
--[[
Comment
]]
"
, but also
"
--[===[
Comment
]===]
"
where the number of "="s must match.

I've tried using a span like so:

	<Span color="Comment" multiline="true" begin="--\[(=*)\[" end="\]$1\]"/\>

but this does not work.

Is it possible to use a group captured in the "begin" in the "end"?
And if not is there another way to accomplish this?