[css-forms-1] How to allow control-value() to be used from an arbitrary element?

[nt1m]

If control-value() is used from a pseudo-element for a form control, it's pretty obvious how to look up the element to get the value from. It's less obvious if you use it on an arbitrary element.

One suggestion is to add an implicit link on output elements, but I'm curious if we should/could add another mechanism in control-value()