Sorry I missed the notification. No, unfortunately I won't have time anytime soon, I should have said so earlier. You are free to take my code and fix it if you want.

I splitted the commit, however, some tests didn't run on my machine because of some weird include errors in mediawiki, so I'm not sure if everything works, sorry.

I merged all sequences of <mi> which share the same style attributes.

Is there a rationale for not having a MMLleaf::setText method, or is it an oversight ? This forbid post-processing of the produced tree, for example.

@Physikerwelt I'm working on it, sorry for the delay.

It would be easy to merge every sequences of alphabetical Literals inside \operatorname (and also inside \textit, \textrm, etc.), by modifying the squashLiterals method of TexArray. However it would not work for macros that returns text (like \gamma): for that, we would need to squash Literals after the macro expansion, so either we would need a new phase of compilation, or we must squash the resulted MathML (which would be difficult). But I think that this is not a problem, because greek letters and other non-standard letters inside \operatorname should be very rare, no ?

@SalixAlba I don't see anything on Optical metric, which version of Chrome are you using? It seems it is a browser bug. If so, shouldn't it be reported upstream?

So, I did some tests with the MathML output and it seems to work fine, even with unicode, but I had to use the package unicode-math, as the symbols provided by external packages did not work (I think that it should be fine with the ones of the ams* packages). From what I understood, \mathrel, \mathord, etc. determinate the spacing and the output type (mi or mo) of the symbol, and by default non-letter symbol are put in a <mo> tag. It doesn't exactly solve this issue, but I think it is good enough: for example, \mathbin{A} yields <mo lspace="0.222em" rspace="0.222em">A</mo> and \mathbin{AB} yields :