The simulation library is a collection of components which will aid you in testing and verifying your designs. Components in this library are decidedly not synthesizable and should never be included in a final design. A lot of the components use actsim's capability to call external C functions from within CHP code.
All components of the simulation library can be found within the sim namespace. There are several sub-namespaces which contain components which fall under the same group. You can access all these components by importing the sim namespace.
import sim;