[NTG-context] define math function with \, inside

Hi all, I wanted to define a custom math function (similar to log etc.) for argmax. However, I wanted to have a small space between "arg" and "max" and limits should work properly. I am using a up-to-date LMTX installation. Without the first constraint it's easy:

% old way: \definemathcommand[argmax][limop]{\mfunction[argmax]} % new way, discoverd by looking into math-def.mkxl \definemathfunction[argmax]

However, both methods do not work if I want to have "arg\,max" printed (error about \endcsname missing). With mkiv the first method works and can also be found in the wiki[1]. What's the current way to define such a custom math function? Thanks! Stefan [1]: https://wiki.contextgarden.net/Math/functions