Part groups are created by the user, and are basically a way to categorize parts for the auto-wiring, and for overall organization of the vehicle.
Groups can be hidden in the editor (plumbing and attachment).
They may be selected to be applied to parts before they are added, by selecting the group from a drop down in the part list
They may be assigned to existing parts by right-click menu
A part group extends to all machines contained by the part, including plumbing machines. It could be interesting to actually have machine groups, but this may be extremely confusing for users, as a single part could end up in many machine groups.
Part groups are created by the user, and are basically a way to categorize parts for the auto-wiring, and for overall organization of the vehicle.
Groups can be hidden in the editor (plumbing and attachment).
A part group extends to all machines contained by the part, including plumbing machines. It could be interesting to actually have machine groups, but this may be extremely confusing for users, as a single part could end up in many machine groups.