Enumeration Facets
SQL Server rejects XML schemas with types that have pattern facets or enumerations that violate those facets.
Example
The following schema would be rejected, because the featured enumeration value includes a mixed-case value. It would also be rejected because this value violates the pattern value that limits values to only lowercase letters.
CREATE XML SCHEMA COLLECTION MySampleCollection AS '
<schema xmlns="http://www.w3.org/2001/XMLSchema" targetNamespace="http://ns" xmlns:ns="http://ns">
<simpleType name="MyST">
<restriction base="string">
<pattern value="[a-z]*"/>
</restriction>
</simpleType>
<simpleType name="MyST2">
<restriction base="ns:MyST">
<enumeration value="mYstring"/>
</restriction>
</simpleType>
</schema>'
GO