I want to adjust the kerning between f' in math mode (and other pairs) across the entire document. I found https://tex.stackexchange.com/a/219881/54601, which is exactly what I want but for text mode, and indeed it does not work for math mode. How do I do it? I do not want to have to create a macro for every pair. I would like to use XeTeX if possible. Is it? I have already gone through like a hundred different questions on TeX SE and I could not find an answer to my question.
Here is an example that needs fixing. No, I do not want to use any other font, and no, I do not want to fix each instance manually nor use a macro. Is LaTeX or XeTeX is incapable of fixing such a simple typographical issue?
\documentclass{article} \usepackage{unicode-math} \setmathfont{xits-math.otf} \setmathfont[range=\mathit]{Times New Roman Italic} \begin{document} $f'$ \end{document} 


\setmathfont[range=\mathit]{TeX Gyre Termes Math}there would be no problem.