The reference to the desktop spec was what I was looking for, wonder why that doesn't appear in the docs, it used to? Unfortunately it is not explicit about leading spaces either, but [the docodementation](https://gitlab.gnome.org/GNOME/glib/-/blob/main/glib/gkeyfile.c#L1277) says leading spaces are ignored, so it won't matter if the user only deletes a `#` and leaves a space. Still probably best to just comment settings with a `#` no space.