If thats the case then the schema is a bit ambiguous.
[quote:e7343b6206][b:e7343b6206]From W3.org – XML Schema Part 0: Primer Second Edition[/b:e7343b6206]
When an element or type is declared to be \”abstract\”, it cannot be used in an instance document. When an element is declared to be abstract, a member of that element’s substitution group must appear in the instance document. When an element’s corresponding type definition is declared as abstract, all instances of that element must use xsi:type to indicate a derived type that is not abstract.
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If both the element and its type are marked as abstract the you have a small problem. You can’t use <GeneralDetail> or <SpecificDetail> because they are types not elements and you can’t use <Detail> because it is marked as abstract.
Can you refer this back to the schema author.
I just did a quick check, it looks like Biztalk ignores the abstract attribute on the element if there is no substitutionGroup.
It creates a Detail node with the xsi:type set and this passes instance validation even though the Detail element is marked as abstract.