(Part of #5384 - MathML Core related CSS)

Mathematical rendering contains lots of 'scripted' concepts - that is, subscripts, superscripts, underscripts, overscripts, tensors and so on. The way that they are positioned is contextually dependent. A (simple) example of this can be seen in the case of exponents within a square root vs normally. The example below, illustrates this, in which the exponent is tighter to the base when inside a square root.

TeXbook (and the spec algorithms) refer to this as "cramped" style. MathML-Core introduces the math-shift property to expose these two modes with values normal (default) and compact. Recommended UA styles apply the common rules, but leave authors the ability to tweak and extend.