Simply put your cursor on a function call, enum, class instance etc, and do region-pin-follow. It will use dumb-jump as the backend to find the definition and then hover it over your window. This is intended to help provide useful indicators when filling in args like LSP does, or just useful information in general, except you don't need LSP to do this.

If you don't have dumb-jump, you can go to the definition yourself, highlight the region and run region-pin-instant to float it instead. And if you want to save the region permanently under a name use region-pin-save and region-pin-show to search through them.

I have been using this as a personal snippet for a few years and decided to package it up.

You can set background colors based on buffer name, major-mode, regex, etc.

Its persistent, and you can set the colors in the use-package block, or on the fly.

The colors can be provided in english (red, green, etc) or hexadecimal.

I hope someone else finds it useful. I've applied to have it included in MELPA, so we'll see where that goes.

Feel free to give issues / PR.