...unless we find some legitimate use case. Currently it's supported via `pcmk__xml_update()` -> `copy_in_properties()` -> `expand_plus_plus()`.
It's a pain to read and maintain, but more importantly CIB replace operations don't treat `"<attr>++"` and `"<attr>+=<int>"` specially. They set the values as unexpanded strings.
Ideally, a modify operation and a replace operation should both set the same attribute value in the CIB for the same input attribute value.