Should `bitset` and `clist` support `V`-type expansion?

[muzimuzhi]

interface3.pdf says V-type expansion can be applied to bitset and clist variables, but expl3.pdf says no, because they both don't have a \<var>_use:N function.

• interface3.pdf (2024-07-20), sec. 1.1 Naming functions and variables, page 4 https://github.com/latex3/latex3/blob/5ada012ff4c9acd53e9b9814c8a860a84d84b73c/l3kernel/doc/source3body.tex#L305-L320
• expl3.pdf (2024-07-20), sec. 4 Expansion control, page 10 https://github.com/latex3/latex3/blob/5ada012ff4c9acd53e9b9814c8a860a84d84b73c/l3kernel/expl3.dtx#L650-L656

The code behavior is that they both can be V-expanded, though that relies on their current implementation.

I think for clist a new \clist_use:N <clist var> which can be used as a quicker version of \clist_use:Nn <clist var> {,} (a ,₁₂) is useful. A \bitset_use:N, which if defined would do exactly the same as \bitset_to_bit:N, seems less desired.

It's arguable whether a clist or bitset delivers a single value, which was the reason used to reject prop and seq in https://github.com/latex3/latex3/issues/1466#issuecomment-1953156467. Considering clist and bitset do both have more unified serialisation forms than prop and seq, maybe the \<var>_use:N restriction can be relaxed or modified.

[muzimuzhi]

In interface3.pdf/source3body.tex,

• clist was one of the original members of the list, see 1a7615ef (Doc e-type at start of interfaces3, and new variable types (fixes #528) [ci-skip], 2019-02-10)
• bitset was added to the list in e1ab799d (Add bitset to the lists of variabe types, 2023-11-16), when bitset was moved to l3kernel.