Adding a new fluid
Adding a new fluid is very straightforward and requires simply instantiating a RebarFluid and then registering it.
You should add a temperature to every fluid you register. Above, the FluidTemperature.NORMAL temperature is assigned to plant oil using addTag. The reason addTag is used is because fluid temperature is a fluid tag. This is explained further in the fluid tag docs
Hiding fluids from the guide
You can prevent fluids from showing up in the guide as follows:
Base ingredient fluids
You may wish to mark a fluid as a 'base ingredient', meaning that in recipe ingredient calculations, the fluid will not be broken down any further. You can do this as follows: