Requests for comment/Reduce math rendering preferences

Proposal
This is a requests for comment about reducing math rendering preferences.

RFC closed and accepted. Options eliminated but still need to add baseline shift per https://bugzilla.wikimedia.org/show_bug.cgi?id=32694.

Background

 * wikitech-l thread
 * follow-up threadlet
 * follow-up threadlet
 * w:Wikipedia talk:WikiProject Mathematics/Archive/2011/Jul
 * w:Wikipedia talk:WikiProject Mathematics/Archive/2011/Jul

Bug 24207 requests switching the math rendering preference default from its current setting (which usually produces a nice PNG and occasionally produces some kinda ugly HTML) to the "always render PNG" setting.

I'd actually propose dropping the rendering options entirely...


 * "HTML if simple" and "if possible" often produce horrible ugly output that nobody likes, so people use hacks to force PNG rendering. Why not just render to PNG?
 * "MathML" mode is even MORE limited than "HTML if simple", making it entirely useless.
 * nobody even knows what "Recommended for modern browsers" means, but it seems to be somewhere in that "occasionally crappy HTML, usually PNG" continuum.

So we're left with only two sane choices:


 * Always render PNG
 * Leave it as TeX (for text browsers)

Text browsers will show the alt text on the images, which is... the TeX code. So even this isn't actually needed for its stated purpose. (Hi Jidanni! :) lynx should show the tex source when using the PNG mode.)

The feedback I've received so far indicates that the 'leave as tex' option is mostly used in concert with gadgets or user scripts to run MathJax rendering.

But the immediate fix of removing those extra unwanted options seems like it can be an easy win to reduce complexity and inconsistency in the math rendering behavior.

Supplementary possibilities
Integrating MathJax-style rendering automatically in supported browsers could be useful, and might eliminate the need to keep the 'leave it as tex' option.

Not covered
Full core integration of alternate rendering technologies (eg replacing Math + texvc with Wikitex etc) are not considered at this time.

But collecting specific information to make a future change decision is useful!
 * texvc currently cannot send baseline information which is necessary to properly position the image relative to text
 * -> future image rendering should either improve texvc or replace it with a tool that already does this
 * blahtex PNG rendering apparently has this
 * blahtex MathML rendering should also be nicer
 * -> reconsider blahtex in more detail at some point!

Implementation
Key:
 * 1) remove the following options from math preferences (done in r104498):
 * 2) * 'HTML is very simple or else PNG'
 * 3) * 'HTML if possible or else PNG'
 * 4) * 'Recommended for modern browsers'
 * 5) * 'MathML if possible (experimental)
 * 6) Have all of those options, where already present, fall back to the 'Always render PNG' option.

Possible secondary:
 * 1) remove the math rendering preferences entirely, and always send the PNG image
 * 2) create a common gadget, extension (Extension:MathJax?), or built-in feature to enable MathJax or similar rendering to replace the image alt text, letting people transition to that mode (started on r104521)