Analog of katex htmlData command for enriching math with dom dataset values

Created by: dainiak

Currently MathJax supports enrichment of formulas with html id and css class attributes. Sometimes it is convenient do add some extra data to an element which does not naturally converts into e.g. css class assignment (e.g. attaching data-fragment-index to parts of math formula when making a reveal.js presentation).

Recently KaTeX added an HTML extension which supports \htmlData macro to add “data-xxx” attributes to the created math elements as well. It would be great so see this feature in MathJax as well.