2.2.3 [W3C-XSS] Section 3.8.6, Constraints on Model Group Schema Components

V0012:

The specification states:

 Schema Component Constraint: Element Declarations Consistent
  
 If the {particles} contains, either directly, indirectly (that is, within the 
 {particles} of a contained model group, recursively) or ·implicitly· two or 
 more element declaration particles with the same {name} and {target namespace}, 
 then all their type definitions must be the same top-level definition, that 
 is, all of the following must be true:
 1 all their {type definition}s must have a non-·absent· {name}.
 2 all their {type definition}s must have the same {name}.
 3 all their {type definition}s must have the same {target namespace}.

MSXML6

If a model group implicitly contains an element declaration that has the same {name} and {target namespace} properties with a directly contained element declaration, it does not cause an error.