What About anySimpleType? (XML Schema)

4.7. What About anySimpleType?

We have now covered all the predefined datatypes except one, which is an atypical type: anySimpleType. This datatype is a kind of wildcard, which means, as expected, that any value is accepted and doesn't add any constraint on the lexical space.

anySimpleType has two other characteristics that make it unique among simple types: users' simple types cannot be derived from it and its properties, and its canonical form is not defined in the Recommendation! These characteristics make it a type that should be avoided, except when the rules of a derivation (which we will see in the next chapter) require its usage.