The docstring for the section parameter in the Edit API currently says:

Section number. 0 for the top section, new for a new section.

I'm told (and comments in other tasks seem to confirm) that this is misleading. Wikipage sections can have non-numeric identifiers due to transclusion (T-123), and apparently the API accepts these as is. In other words, the docstring should be something like:

Section identifier. 0 for the top section, new for a new section. Often a positive integer, but can also be non-numeric.

The key part being to change the nomenclature to "identifier" rather than "number"; the rest is just to make it easier on users of the API docs (I've seen people with +2 try to cast these to int).