xelatex, lualatex, and applying stylistic sets to part of a word in Arabic

[mayer-goldberg]

I bought the beautiful Arabic font "Zuhair Albazi Naskh" that supports many stylistic sets. One of these has to do with the two forms for the kaaf:

When I apply the relevant stylistic set to an entire word, it renders all the kaaf in the same style:

But if I would like the first kaaf to be in one style and the second kaaf to be in another style, I need to apply the stylistic set to part of the word. In that case, the letters do not connect properly:

Now the author of the font tells me this font works well in InDesign, but the same phenomenon happens in MS Word... I've tried to render this both in xelatex and lualatex, and both cause the word to "split", that is, to recognize the first half as a separate word. Before I despair and move on, is there anything I can do, in xelatex or lualatex, to get this "to work", namely, to be able to apply a stylistic set to a part of the word without causing the renderer "to think" that the first part "has ended"?

[alerque]

This is really a question for TeX experts, not HarfBuzz. Have you tried asking an https://tex.stackexchange.com/? It is pretty unusual to apply different stylistic sets inside a single segment that must be shaped in one pass. I think it is possible in TeX but I suspect you have to do some serious contortions to convince TeX to ask for it all in one go instead of piece by piece where your style boundaries fall.

[khaledhosny]

HarfBuzz supports enabling features for sub-ranges of the input text, but neither XeTeX nor LuaTeX make use of this. So this is a question/issue for the TeX engines.