I'm making subtitles for math videos in which super/subscript, square root, big fractions and 2x2 matrix are common. Currently I use {\pos} to manually adjust the position if there's no specified super/subscript Unicode character; use a tick ✓ to substitute square root.

I propose to add {\sub}, {\sup} and {\sqrt} tag. For the sake of readability, and avoid introducing math shaping engine, nesting of those three tags (which is rare in subtitle) could be forbidden, e.g. a^x^2, a^(x_3), a_x_4, sqrt(x^4) and sqrt(sqrt(16)). If necessary I will just write one layer in plain text, for example sqrt(x{\sup1}4{\sup0})

However the combination of {\sup} and {\sub} should be allowed, e.g. SO_4^2+ could be either expressed as SO{\sub1}4{\sub0\sup1}2+{\sup0} (literally the second) or SO{\sup1}2+{\sup0\sub1}4{\sub0} (literally the third). Moreover, when {\sub} and {\sup} are appended to the same character, the left border of {\sub} and {\sup} should be aligned (the left one).

Furthermore, with some {\fsp} hacks, big fractions and 2x2 matrix like these two

could be descibed by {\sub} & {\sup} if they can append to a space.