Similar to my reply to Bramus, but it could be a pure CSS selector (thanks to :has) that has a reference to the current element:

for="form:has(:scope) [name=field]"
for=":scope + *"
for="body #x"

I've been wanting this for ages. Pretty much everything on a web page is context dependent, so essentially if you have a way to define the context and then execute a selector pattern in that context, you could do almost anything.

for="form:has(:scope) [name=field]"
for=":scope + *"
for="body #x"

Tit for tat has been shown to be the best strategy in game theory.

Do you mean in terms of verbiage or how it functions?