2.1.2 [W3C-XSS] Section 3.3.4, Element Declaration Validation Rules
V0002:
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4 If there is an attribute information item among the element information item's [attributes] whose [namespace name] is identical to http://www.w3.org/2001/XMLSchema-instance and whose [local name] is type ... 4.2 The ·local name· and ·namespace name· (as defined in QName Interpretation (§3.15.3)), of the ·actual value· of that attribute information item must resolve to a type definition, as defined in QName resolution (Instance) (§3.15.4) – [Definition:] call this type definition the local type definition;
MSXML6
An attribute information item that does not resolve to a valid type does not cause an error.