Yet more questions.
Question 1. The various counter-creation macros in expl3 work like
\newcount. There doesn't seem to be anything like \newcounter, for
creating something with a user-facing \the<counter>. Should counters
that go near the user stick with \newcounter for the moment, or should
one define \c@<counter> and \the<counter> "by hand" so that things look
the same for the user? I guess this is partly a philosophical question!
Question 2. Why is \clist_map_break:w "weird"? It doesn't take an
argument from a use point of view, so I'd have expected \clist_map_break:.
Do tell me to stop if I'm asking too much!