When an element/attribute is validated against a union type, PSVI has [member type definition] property to indicate which member type was used. But when it's validated against a list type whose item type is a union, there is no way (from PSVI) to find out which member type of the union was used to validate a given item in the list.

Suggest to add a new PSVI property [member type definitions] (a list of (atomic) simple type definitions) to expose such information in PSVI.