Cycles 4D has a number of tags for various functions. These are:

Tag Function
Attribute Tag Used with the Attribute node to access certain types of data - see here for an example
Camera Tag Gives control over the camera when used in Cycles 4D
Curve Tag Required when rendering splines in Cycles 4D
Instance Tag Used when generating geometry with X-Particles
Light Tag Provides control over light objects; use this instead of the controls in the light object user interface
Object Tag Cycles 4D's equivalent of the Cinema 4D compositing tag