gtksourceview: keyword-char-class example

["Mark" <mark dibsco co uk>]

Hello

I am working on a language definition file and would like to modify the 
default word boundary regular expression. I believe that this can be done 
using 'keyword-char-class', but I can't work out what the syntax should be 
and can't find any examples.

I'd be grateful if anybody could point me in the right direction.

Thanks

Mark