Question about xsd:extension

[Amol]

Hi all,
I have a case where I have a element that can appear under multiple
elements
e.g.
<AppFunctions>
<UseTemplate name="1"/>
<MethodSet name="2">
<UseTemplate name="3" />
<MethodCall name="4" />
</MethodSet>
<MethodSet name="5">
<MethodCall name="6" />
</MethodSet>
<UseTemplate name="7" />
</AppFunctions>

I would like a way to define a root element which has just the
UseTemplate element and then derive 2 elements from it "AppFunctions"
and "MethodSet" which extend it to add further elements to it. This
elements in the derived elements need to unordered and can occur
multiple times. This is what I came up with:

<xs:complexType name="UIElementType">
<xs:choice maxOccurs="unbounded">
<xs:element name="UseTemplate" type="UseTemplateType" minOccurs="0"
maxOccurs="unbounded" />
</xs:choice>
</xs:complexType>

<xs:complexType name="AppFunctionType">
<xs:complexContent>
<xs:extension base="UIElementType">
<xs:choice maxOccurs="unbounded">
<xs:element name="MethodSet" type="MethodSetType"
maxOccurs="unbounded" />
</xs:choice>
</xs:extension>
</xs:complexContent>
</xs:complexType>

<xs:complexType name="MethodSetType">
<xs:complexContent>
<xs:extension base="UIElementType">
<xs:choice maxOccurs="unbounded">
<xs:element name="MethodCall" type="MethodCallType" minOccurs="0"
maxOccurs="unbounded" />
</xs:choice>
<xs:attribute name="name" type="xs:string" use="required" />
</xs:extension>
</xs:complexContent>
</xs:complexType>

This definition is allowing me mutiple UseTemplate nodes directly under
AppFunctions but once I add a MethodSet node under AppFunctions, it
does not allow any UseTemplates anymore.

Thanx in advance,
Amol.