IsPlug

Flag:	IsPlug
File(s):	Rules(md).ini
Values:	Boolean values: yes or no, true or false, 1 or 0
Default:	false
Applicable to:	BuildingTypes
Logic related to IsPlug, as a whole or in part, is obsolete in Red Alert 2 and/or Yuri's Revenge.

Can be set to 'true' or 'false' and specifies whether or not this BuildingType is a 'plug' (upgradeable structure) and thus is considered by the AI when choosing a target for the Weather Storm or Nuke.
Residual from Tiberian Sun although the game does perform a check to see if a structure is named GAPLUG - if it is it is then hard coded to have its Foundation= over-ridden so that it is set to Foundation=2x3 (see the ART.INI Guide)
which may invoke some additional function although this has yet to be established.