Surprisingly it’s not easy, and depending on the field it can be quite challenging. The reason for this is that TeX captures the visual aspects of typesetting,

Surprisingly it’s not easy, and depending on the field it can be quite challenging. The reason for this is that TeX captures the visual aspects of typesetting, not the semantic meaning of the mathematics. A simple example is ‘\sum’ which provides no way to capture the expression being summed over - because that’s not necessary for typesetting. That’s not the case in, say, MathML. Writing MathML is no fun though because mathematical formulae are visually ambiguous and we rely on the context to know how to read them, e.g. does ‘f(x - 1)’ mean function f called with argument x - 1, or does it mean variable f multiplied by x - 1?