For example in a video game your player, monsters, health potions, and attacks could all have the code for HealthComponent as a part of their virtual file. And updating the HealthComponent would affect the raw file so the virtual files would have the updates automatically. Yeah you can open dozens of editor tabs or always use jump-to-definition, but just being able to scroll around or ctrl+f within a restricted set of limited files would be nice.
I mean something that would dump them all into, one contiguous "file" from the editor's perspective. Included components (I don't want to say classes because it could work in a functional language or maybe you just don't include full classes but certain methods) wouldn't have to be coupled to the main class you're editing. Like if you have a decoupled event system you could pull in just the events relevant to the idea you're working on. You could have different views depending on what idea you're working on and save them as their own file.
To use the gamedev analogy again you could have MonsterCombat.view MonsterAI.view MonsterAnimations.view which would all expose different subsets of the Monster class and various related methods from other classes/modules.
Like you could have all of the code from class A except the debug related methods, a few methods from class B, just a few functions from a static MathUtils class, so on.
Maybe your ClassAUnitTest meta-file could include some of the ugliest methods from the class you're testing but not the entire class.