Meanwhile I finished (re)writing the syntax highlighting for diff-files. There are 4 files
udiff.jsf -- for unified diffs
cdiff.jsf -- for context diffs
ndiff.jsf -- for "normal" diffs
_diff.jsf -- all together, for mixed or unknown diffs
I thought it would be faster to process a shorter file in cases where the type of diff is well known, that's why there are files for each diff type, plus one that contains "all of them", so to say. If speed is not affected, '_diff.jsf' can fully replace 'diff.jsf'.
There are also 2 snippets of an 'ftyperc' file, one that uses all 4 abovementioned files and one that only uses '_diff.jsf'. Your choice.
Please try and if you have a suggestion, make a comment here.