The lint.vocabs vocabulary implements a set of words designed to find unused imports. It attempts to ignore USE: and USING: that are a part of a string, postponed with either POSTPONE: or \, and contained inside a Regular expressions.
It can sometimes be easy to lose track of what vocabularies you've imported while iterating over ideas. So to find any vocabularies you feel are unused, you can run:
USING: lint.vocabs ;
"lint.vocabs" find-unused. No unused vocabs found in lint.vocabs.