Unable to get UnhandledAttributes for XmlSchemaChoice Class

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Context : .Net Framwork 2.0, C#, XPSP2,VStudio 2005

hi,

Is this behavior is by design or is it a bug ?
I've found any documentation that mention that fact.
It works fine for the following schema objects, i've tested :
- XmlSchemaElement
- XmlSchemaAttribute
- XmlSchemaEnumerationFacet

I've tried both API i.e. compile schema with XMLSchemaSet and the deprecated
one XmlSchema.Compile

Please do not answer that i can put my custom attribute elswhere it is what
i have made.

I just want to know if
- it is my misundertooding of api
- this behavior is by design
- it is a bug and there is a patch
- it is a bug and there is no patch
- it is a bug and there no plan to fix it today
- ....

Best Regards
Addendum :

XSD Sample

<xs:choice nrdata:dependOn="type">
<xs:element name="fqdn" type="Tfdqn" nrdata:dependOn="type"/>
<xs:element name="ip" type="TIrange" nrdata:dependOn="type"/>
</xs:choice>

[=?Utf-8?B?THVjIEFscXVpZXI=?=]

So it is was my misundertooding of API

To fix that i traversed element using
complexType.Particle
instead of
complexType.ContentTypeParticle;

Thanks to me for answer.