Reverse of "Hide" - Guide? Ghost?

It would sometimes be handy to mark certain geometry as being “permanently” visible and able to be snapped to, even when it’s hidden behind other stuff. As if the “X-ray” mode was on, but only to see the tagged lines/objects.
These could be turned on/off in the same way as you can turn on/off any hidden geometry.

Sounds very similar to this question?

You can use the inference system with visible back edges too.

Similar, but marking an object as “perminatly” visible… If you have ever played any first person games where you can highlight/tag an enemy and no matter where they go, they are outlined through walls and scenery - like that.

This is a global effect to do with viewing a model and showing/highlighting the location of one element within the whole construct.

The other one is a local effect to aid with building the construct in the first place.