Drakal

A predefined set of properties would only go so far in my opinion. Someone might want to add something unique like viscous. A predefined set would be nice, if custom properties were allowed as well. Possibly even putting more than one property to each liquid as well, like a flammable viscous liquid.

A nice feature to add to the liquid API is assigning tags to each liquid. It may seem redundant but hear me out. If you tag Lava as "igniting" or something similar, Xycraft Multitanks could read that, and if it was built with flammable blocks, they would catch on fire, if the tag is coded for. Now, you ask, why not just code that in for lava itself? Well what if a new mod came along and added another liquid that could cause things to catch on fire? If that one was tagged "ignitable" those wooden xycraft tanks would catch fire to that liquid as well, automatically, if coded for. Now that is a very specific use case, so here are a couple others. Steam boilers from Railcraft can take liquids if you build them right, and essentially take a whitelist of liquids in order to burn in it. If you tag a liquid as "flammable" Railcraft could then use it to power that steam boiler. If you tagged the steam resulting as "gas" you could compress it down, like Thermal Expansion liquiducts do, which are hardcoded for. If you tagged a liquid as "acid" whatever storing it could take advantage of the tag and slowly decompose. Things like water could do without a tag and then at the same time cause no benefits or ill effects. Its a small change but a nice one should a new mod want to add a liquid, and tag it right, it could be used with different machines in the game already. Tagging vanilla liquids would be smart as well so mods don't need to hardcode certain liquids that can and can't be used in it, and just blacklist a whole tag or whitelist certain ones.