2.1.4 [W3C-XSS] Section 3.10.6, Constraints on Wildcard Schema Components


The specification states:

 For a wildcard's {namespace constraint} value to be the intensional union of two other such values (call them O1 and O2): the appropriate case among the following must be true:
      1 If O1 and O2 are the same value, then that value must be the value.
      2 If either O1 or O2 is any, then any must be the value.
      3 If both O1 and O2 are sets of (namespace names or ·absent·), then the union of those sets must be the value.
      4 If the two are negations of different values (namespace names or ·absent·), then a pair of not and ·absent· must be the value.


When a wildcard's {namespace constraint} value is the union of two values (O1 and O2), if either O1 or O2 is any, the value is not always any.