How does Free Support work?

[swang30]

There are two separate types of bonuses, Free Unit Support, and Free Supply. one is MOD_EFFECT_FREEUNIT_BONUS and MOD_EFFECT_EXTRA_SUPPLY.

The former is given by things such as Strape's Palace and have a base from government type. Some mention it's a national mod, some do not. However, since it's the same bonus type, I assume it's all national.
1) Is this free upkeep just money, or money and other resources?
2) How is it assigned? Most expensive first? Most overall resources? Least?

The latter is given by things such as Food Preservation, this extra supply seems to be just food. and I can't tell if it's national. Questions:
1) Is this in raw food points? or 20 units worth of food?
2) Is this national?
3) How is the free food assigned?

Finally, is there any place I can look at either a summary or detailes of the logistics of supply/upkeep?