How do I correctly typeset metastable radionuclide symbols? Does anyone know if there is an officially sanctioned way to typeset symbols like technetium-99m (99Tcm or 99mTc)? I have seen both, although in more recent publications, I think, the latter predominates.

For my part, it looks somewhat wrong to place the symbol for metastable in the position you'd normally expect the charge. How would you write the ion, 99Tcm+? That looks quite clumsy.

So does anyone know if there's some IUPAC (or similarly authoritative) guidance on this?
According to the international standard ISO 80000 Quantities and units – Part 9: Physical chemistry and molecular physics, Amendment 1, a metastable nuclide is indicated by adding the letter m (in roman type) to the mass number of the nuclide, as in the following examples:

$$\mathrm{^{133m}Xe}$$
$$\mathrm{^{99m}Tc^+}$$