Wouldn’t it be cool if placeholders were capable of impersonating a selected two- or three-character string rather than just deactivating themselves when more than one character is selected? That would make it easier for us to test kerning pairs such as AV in context.
I guess there would have to be a limit to two or three letters to avoid accidentally blowing up the screen with a «Select All».
You’d need a dedicated (different) placeholder for that, though. My suggestion would work with the existing placeholder and fill a functional gap that is currently going unused.
For this, have you tried Kernkraft already? It is supposed to help you with exactly this: See kerning pairs in context (without the need of saving/handling lots of sample strings or lists).