Yes, that's correct. This is a smart-margin feature.
It wouldn't be too hard technically and probably desirable to annotate individual elements of an equation block
(for example, consider highlighting a term being moved from one side of the equal side to the other in two successive equations)
However, I've run into two design / UX issues when considering this case:
- in the final HTML, how would the user interact with the annotation:
- to see that an element is annotated (needs to work with nested annotations, with multiple annotations, etc)
- to see which elements are concerned by the currently-displayed annotation (without interfering with the "is annotated" styling of the other elements of the equation block)
etc
- how would the writer specify the annotation, in a way that isn't too disruptive of their normal workflow?
- this is the bigger issue for me. without a rich-text editor which supports highlighting of individual math elements, I don't know how to handle this
even If I had a great answer, there remains the issue of hacking it inside of MathJax.
At this point, it might be better to actually fork their code, instead of writing something a posteriori
I'd love to have it as a feature someday, but it's in the distant future.