The double-hyphen prefix in custom properties came to life, basically, as an empty vendor prefix, i.e. -vnd-ident wherein vnd is the empty string.

Much later, <dashed-ident> was specified explicitly for author-defined private idents (not just properties). However, its documentation suggests that third parties, e.g. frameworks and preprocessors, should again include vendor-identifying pseudo-namespaces, but now with two hyphens in front!

Even better, it should use @--library1-custom, (…)

Can we please change this (back) to a single hyphen? Start a simple namespace registry if you must.

I understand that <custom-property-name> as used in var() could remain being restricted to double-hyphen prefixes, but other places could accept vendored idents as well. Actually, I would like vendored custom properties, too, e.g. for industry-standard color names like -ral-5002 #817 or media sizes like -iso-a2 #328 and -vesa-xga.