Mathematics can be made active: $$\sin^2\theta + \cos^2\theta \mathrel{\bbox[position:relative;z-index:105;" onclick="message()]{\color{blue}{=}}} 1$$ or $$ (2x+3)(x-5) = \mathord{\rlap{\bbox[position:relative;z-index:105" onclick="foil()"]{\color{blue" ID="question}{\hbox{?}}}}} \style{visibility:hidden" ID="poly"}{2x^2 - 7x - 15} $$