Jean-François B.

ah ok that bit of source2e (code of `\SetMathAlphabet@`, `File r: ltfssdcl.dtx Date: 2016/02/18 Version v3.0r 213`): ``` If the math alphabet was defined via \DeclareSymbolFontAlphabet we have remove its...

The root cause is that `\@fontswitch` has kept its standard meaning but `\use@mathgroup` got modified. I can propose a PR to modify `\@fontswitch` so that it does what could be...

Actually there is already a `\__um_fontswitch:n` used by patched `\operator@font`. What is lacking is a hack of `\@fontswitch` akin to that.

Proposed patch I don't have enough experience and usage of unicode-math to test this seriously this is why I don't make PR but just propose it here in the form...

Added note: the two lines involving `\__ummath@bgroup` and `\__ummath@egroup` look suspicous because in `unicode-math-code.pdf` I find `\@@math@bgroup` used only once, in the definition of `\@@_fontswitch:n`, and it never gets a...

ah I see of course! The unicode-math sources copied over `\@@math@bgroup ` from LaTeX kernel but the `@@` got transformed... This is a bug...

So naturally, my user hack should read ```latex \makeatletter \ExplSyntaxOn \def\@fontswitch #1#2{\ifmmode % ORIGINAL KERNEL CODE % \let \math@bgroup \relax % \def \math@egroup {\let \math@bgroup \@@math@bgroup % \let \math@egroup \@@math@egroup...

Sorry for spam but only to add to passers-by that there is a difference between the `\__um_group_begin_frozen:` and `\__um_group_end_frozen:n` with meanings respectively ``` \begingroup \protected\long macro:#1->#1\group_end: ``` and the LaTeX...

arggh, > now simply be circumvented I meant NOT simply be circumvented.

> In a l3docstrip file you can write `\@@@@math@bgroup` to result in `\@@math@bgroup` in the .sty file. I trusted you guys had foreseen every possibility `:)` > The differences that...