Ok, I've done this and it's now active in the latest SVN.
I only modified the core schema in assets/xml/buildings/C2C_CIV4BuildingsSchema.xml, so if you need it in a module be sure to update the schema copy there also. The extra schema element is:
Code:
<ElementType name="BuildingExtraCommerce" content="eltOnly">
<element type="BuildingClass"/>
<element type="CommerceType"/>
<element type="iExtraCommerce"/>
</ElementType>
<ElementType name="GlobalBuildingExtraCommerces" content="eltOnly">
<element type="BuildingExtraCommerce" minOccurs="0" maxOccurs="*"/>
</ElementType>
I just did a simplistic test, adding this to an existing building, and checking that when one is built it grants the culture/research effects on the building player's forges and granaries everywhere:
Code:
<GlobalBuildingExtraCommerces>
<BuildingExtraCommerce>
<BuildingClass>BUILDINGCLASS_FORGE</BuildingClass>
<CommerceType>COMMERCE_CULTURE</CommerceType>
<iExtraCommerce>1</iExtraCommerce>
</BuildingExtraCommerce>
<BuildingExtraCommerce>
<BuildingClass>BUILDINGCLASS_GRANARY</BuildingClass>
<CommerceType>COMMERCE_RESEARCH</CommerceType>
<iExtraCommerce>1</iExtraCommerce>
</BuildingExtraCommerce>
</GlobalBuildingExtraCommerces>
Note - at least for now use of this tag should be restricted to wonders (national or great), because if you put it on a normal building then EACH one you build will grant the global effect!
Also note that I decided to call it 'GlobalBuildingExtraCommerces' not just 'BuildingExtraCommerces', to reflect the fact that its effect is in all the player's cities, not just the one the triggering building is built in.
I have updated the building hover text generation to take account of this new tag also, but not yet updated the AI to evaluate it (will do that once the Wonders are in - let me know)