While developing a plugin for WordPress I was having trouble linting CSS files in PHPStorm. One file in particular was giving hundreds of false positives for errors related to paths:
This bothered me. I wanted to fix the reported errors but the reporting was wrong. Most of the time there was nothing to fix. After much fiddling I discovered files under a folder marked as Resource Root can be referenced as relative:
Low and behold the errors became real! Oh crud, time to fix.
Source:
https://www.jetbrains.com/phpstorm/help/configuring-folders-within-a-content-root.html