Union of Union with facets

I have a question about the section in the Xml Schema structures spec
about Union Schema Component (under 3.14.2). It mentions that the actual
value of member type definitions is formed by replacing a union type
definition in the explicit members with members of their respective
member type definitions.

But it doesn't mention anything about the case where a restriction of a
union (with some facets, e.g. enumeration) is a member type of another
union. How should the facets be applied to the parent union while
resolving the child union to its simple type definitions?

Thanks,
Zafar Abbas