Those three nodes are modified in the scene only, actually those three nodes are simple nodes, but they are created by MEL commands by the program itself, as a matter of fact, if you get to know the Hypershade, and you accidentaly delete one of the nodes, you can always create a new one, and connect it to the other two. They are governed by the same Shader Networks laws, just like all the other shader nodes. Don´t worry, open a new scene and you´ll see.