Validating XML Tag Contents but not the Tags?

[Jim Whitehead]

Hello,

We would like to use several tags that are ignored for validation purposes,
but whose content is not ignored.

That is, given an XML schema containing something like this:

<--! These tags would be allowed anywhere in the document, but ignored for
validation purposes -->
<xs:element name="ADD"/>
<xs:element name="DEL"/>
<xs:element name="OTH"/>

<xs:element name="Reference">
<xs:complexType mixed="true">
<xs:sequence>
<xs:element name="XXX"/>
<xs:element name="YYY"/>
<xs:element name="ZZZ"/>
</xs:sequence>
</xs:complexType>
</xs:element>

We would like something like this to be a valid document:

<Reference xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="test.xsd">
<XXX/>
<DEL><OTH><YYY/></OTH></DEL>
<ADD><ZZZ/></ADD>
</Reference>

Is there a way to do this?

Thank you very much for any insight you can provide!

Jim