On occasion, questions / answers / comments on physics.se deal with chemical elements. An example for this may be to discern between the isotopes of carbon, C-12, C-13, and C-14. I would like to suggest an expansion of the acceptable syntax to write, e.g., $^{12}\mathrm{C}$. At present, I know $^{12}\mathrm{C}$ yields a visually reasonable result, but there may be more efficient approaches (by the number of key strokes) that I'm not yet aware off.
On chemistry.se, this problem was solved by adding mhchem to the "vocabulary" of mathJax. For the isotope mentioned above, the syntax would then simplify to a shorter input of $\ce{^{12}C}$.
Additional benefits potentially relevant to the audience of physics.se could be
the easier input of chemical sum formulae. To write e.g., about water, $\mathrm{H}_2\mathrm{O}$ (please, not a mixed roman / italic $H_2O$ as obtained by
$H_2O$), the input would be shortened to$\ce{H2O}$instead of the more verbose$\mathrm{H}_2\mathrm{O}$.Describing recorded measurements like "13 kg", currently entered either as-such in plain text, or formatted
$13~\mathrm{kg}$would be just$\pu{13 kg}$.The syntax permitted on chemistry.se equally allows an input of
$\pu{-17.3 ^\circ{}C}$to yield $-17.3~^\circ{}\mathrm{C}$; to arrive at the same here on physics.se, I type as$-17.3~^\circ{}\mathrm{C}$. The later demands more attention to detail.
Because mhchem brings something special to mathJax not all web browsers understand (well enough) when providing a table of contents about current questions, chemistry.se established the rule to constrain the use of mhchem to the body of questions, answers, comments. So, it is not the panacea for all formatting issues.
\puinstruction is of some different origin, but I'm fine to close the question. $\endgroup$