Default Value for XSD

This question here asks about default values specified in an XSD file. Basically you can say the field "foo" defaults to value "bar"

What I want to know... is it possible to have a field default as the value in another field? If field "foo" is "bar" and "otherfoo" is empty, can I say it's default is the value in "foo"... something along the lines of:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="button" type="button"/>
  <xs:complexType name="button">
    <xs:attribute name="id" type="xs:string"/>
    <xs:attribute name="label1" type="xs:string" default="Go"/>
    <xs:attribute name="label2" type="xs:string" def开发者_JAVA百科ault=label1/>
  </xs:complexType>
</xs:schema>

<button id="1"/>

Where Label1 defaults to "Go"... Label2 defaults to the value in Label1.

Goal is to remove redundancy such as:

<Field Name="State" DataSourceField="State" />

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Unfortunately this is not possible, in fact XML Schema provides little or no support for cross-element dependencies (including validation).