Explanatory pop-ups for variables in equations (just like the ones for references)

[So-Cool]

As a reader I want to hover a mouse over a term in an equation and see its meaning to avoid searching it through the text.

I think that interactive equations -- where each term could get a pop-up explaining its meaning when hovered over with a mouse -- would make reading and understanding them so much easier. Do you think that it would be feasible to implement such a feature?