A general purpose way (into xml) to create paired unit, in witch to specify the unit supporter, who is supported, how many supported and how is (are) supported.
There's a new property called unitsSupported for some of this. See RogerCooper's wiki for details
It seems only for embedded artillery.
renamed the existing property to unitSupportCount.
You're correct it only works for artillery for now... but it's the basis of what you're asking for.