How can a user force the extension to serve MathML (that is, <math …>…</math>) instead of <img>s? En.Wikipedian documentation at w:Help:Displaying_a_formula #Native_MathML is quite confusing.
Topic on Extension talk:Math
I'm pretty sure that as an editor one can't make it do that for other people. That would break the reader experience for the 99% of readers whose device won't render MathML. It's the same way that we don't let editors force the output to have an autoplaying video, even if they really want to; it'd be an anti-user feature.
I feel that Jdforrester_(WMF) missed my point, or I ignore something important myself. The question is not about overriding intended behaviour by planting hacks to wiki code – were it, I’d ask another way, such as “which code can force the extension to switch to MathML?”. The question is about control of the extension by its end user.
What do you mean by "end user"? System administrator? Page editor? Reader?
Who ultimately consumes a wiki page? Reader, of course. Sysadmins definitely don’t fall under the “end” user class unless we discuss tools intended for system administration.