Right now, #textextracts:
* Strips the fallback images from the output of the Math extension; and
* Flattens the `<span style="display: none;">` container element that wraps the `math` element and its children.
The result is that HTML and plain text extracts contain the alt text of the MathML, e.g.
https://en.wikipedia.org/w/api.php?format=jsonfm&action=query&prop=extracts&titles=Planck%20constant
and
> "Ко́мпле́ксные чи́сла — числа вида {\displaystyle x+iy} x+iy, где {\displaystyle x} x и {\displaystyle y} y — вещественные числа, {\displaystyle i} i"
{F7668233}
== AC
* `math` elements (and their children) are stripped.
* `img.mwe-math-fallback-image` and `img.mwe-math-fallback-image-inline` elements aren't stripped from HTML extracts.
* Plain text extracts behave as before, i.e. the alt-text of the MathML markup is still renderered in plain text extracts.
* Video and audio tags are still stripped from HTML extracts
== Testing criteria
* Go to: https://en.wikipedia.beta.wmflabs.org/wiki/Lie_group
* Hover over lie algebra
Expected behavior: lie algebra preview should display all mathematical expressions across browsers