UMLR — Can PrimitiveTypes be user-defined and where?

In 10.2.3 it says that

“A PrimitiveType defines a predefined DataType, without any substructure.”

What does it mean to be “predefined” If a PrimitiveType is predefined, then how can it be defined by a modeler? I recommend that the word “predefined” be deleted from this sentence. In addition, the general impression is that the PrimitiveTypes are only located in the PrimitiveType package and cannot be anywhere else

Though based on a statement in Profile a PrimitiveType could be in a profile, though it couldn’t be used in a model «grin».