How to name string-match selector: `:string`, `:select`, `:equals` or something else?

[aphillips]

See discussion in #425, #431 and elsewhere. We need to choose what annotation signifies the comparison selector.

[aphillips]

In the 2023-12-11 teleconference, the consensus was to use the name :string

[markusicu]

"string" sounds ambiguous; if anything, more like a formatting function name. It would be better to pick a name that sounds related to matching/selecting.