I was wondering if there were any sort of consistent rules or guidelines for how to properly format subscripts on variables? The primary aims should be to have clear meaning, and consistency with what is mostly used in the literature.
A few questions to consider:
- When should subscripts be italic, and when should they be roman? e.g. $x_i$, $x_\mathrm{A}$, $x_1$, $x_\mathrm{CH_4}$, etc
- How should multi-character subscripts be handled? e.g. $X_{Odd}$
- How should long subscripts be handled? e.g. $A_{ChemicalName}$
- When is it appropriate to use symbols for subscripts, and are there any guidelines for doing so? e.g. $A_{triangle}$ vs $A_\mathrm{△}$
- Are there any special rules for things like matrices, functions, chemicals, etc?
I've found some information here that seems to touch on this subject, but it's limited enough that it mostly only suggests that international standards or conventions do exist, without detailing more than a handful of these.