alttext value default aria-label value when present

Created by: jmegginson

MathJax v3.2.0 does not render the alttext attribute value provided to the MathML object as the default (accessible) aria-label.

I have observed that MathJax v2.7.9 worked in this manner and was a good feature at the time.

There are situations when the alttext attribute value can provide clear language to students than MathML markup alone could provide. For example terms like “in equilibrium with…the coefficient...molar concentration of…” applied via the alttext attribute would be more meaningful than "right facing arrow over left facing arrow" when left to automated MathSpeak generation alone.

<math displaystyle="true" xmlns="http://www.w3.org/1998/Math/MathML" alttext="K sub c, equals the fraction with numerator, the molar concentration of uppercase C raised to the lowercase c, times, the molar concentration of uppercase D raised to the lowercase d, and denominator, the molar concentration of uppercase A raised to the lowercase a, times, the molar concentration of uppercase B raised to the lowercase b, where the coefficient, lowercase a before uppercase A, plus, the coefficient lowercase b before uppercase B is in equilibrium with the coefficient, lowercase c before uppercase C, plus, the coefficient lowercase d before uppercase D">...</math>

I propose that when alttext is present within the mathml element MathJax utilizes this as the default aria-label. When the alttext attribute is not present, then users would rely on the default automated MathSpeak generated aria-label.

If a situation occurs where the alttext is not sufficient, users could be given a (new) menu option like "MathML alttext" to choose from along with MathSpeak, ClearSpeak and other options that are currently offered through accessibility menu options.