Any Info on Custom Groups?

[Trachmyr]

I'm currently making a mod to add more diversity and "realism" to ship construction. The first change is to require larger ships to use heavier engines to get the same speed. The problem will be clutter in the ship design screen, as there will be around 10 diffrent engine sizes. However, I noticed that you can create "Custom Groups" for componets, then supposedly use Requirements in VechicleSize.txt to limit which custom Groups a particular design can use.

Now here is my question: How in the world do you set this requirement in the VechicleSize.txt... the descriptions don't conform to the actual entries, and what little is said is quite jumbled. Anyone know or have any clues?

Any help would be appreciated!