Erasable Highlighters
The use case is anything that does not belong to you: a library book, a shared set of readers, a document that goes back into a file. Mark it up, work from it, then clear it. The mechanism is friction heat rather than abrasion, which also means a hot car or a laminator will clear a page you meant to keep. Colours are lighter than permanent highlighters by design. See erasable pens, highlighters and erasable gel pens.