I don't like the idea to magically introduce a '' section since this behaviour would be confusing for interpolation and not particularly discoverable by programmers. Let alone bikeshedding if this should rather be a None section.

Using DEFAULTSECT for this purpose is equally wrong since it would silently inject default values to every section, which may or may not be desirable.

All in all, it comes down to the question whether the programmer expects section-less configuration. If not, the '' section will not be helpful anyway. If yes, then it's desirable to be able to specify a section name for global options at *read time*. Symmetrically, the user could specify which section name to omit during configuration writing. I like that since it's explicit and more composable than a blanket global section. It would also be 100% backwards compatible.

I'll prepare a patch for this idea so we can see how good this API looks like in practice.