UML22 — Section: 7.3.10

The description of Constraint mentions the xor-association that is predefined in UML. There's no place in the superstructure (and infrastructure) where that constraint is defined.

Figure 7.34 shows an

constraint attached to two associations, indicating an Account can be a property of Person or Corporation, but not at the same time. Section 7.3.10 Constraint references “xor” constraint as an example of a UML predefined constraint.
The xor constraint is not explicitly defined in UML. Rather it is used as an example of a constraint between associations as in figure 7.34, and as an example of an expression in section 7.3.18. So the parenthetical remark about xor being an example of a UML predefined constraint in section 7.3.10 should be removed.