How update units automatically works?

In preferences windows, there is a checkbox that updates units automatically, but how does it work?
When I create a C# file with custom enums and when I add a completely new enum type I still can’t get the enum literal from the units. I always have to regenerate units manually, and only then it works.
Is there a way to automate it?

Automatic update updates changes to already added types. If it’s a completely new type, full regen is the only way.

This is one of the major workflow slowdowns that Unity need to solve down the road. Flow Canvas, for example, adds a new type nearly instantly. Much smoother workflow overall. Bolt 2 also had fast extract that checked only for new content, then regened selectively for that.