So that it isn't lost in bug 17465, comment 3 and 4, the grammar and semantics of the <math> tag need to be specified. At the moment, the grammar is somehow defined by texvc, while the semantics differ between TeX source, TeX source as generated by texvc, (still) HTML as generated by texvc and rendering by MathJax.
Personally, I'd opt for TeX as it's stable -- Knuth has made a point of not changing TeX's behaviour so that authors can rely on it. Renderings that differ from TeX's interpretation of input should be considered bugs to be fixed. Note that this doesn't mean that we have to specify TeX's behaviour.