Validating only part of XML document using schema?

Is it possible to write a schema allowing mixing validated XML with just well-formed XML? Case in point is a data transfer application where requests consist of a bunch of meta-data (which we'd like to validate) and record-specific information (which is validated separately from the XML in the business logic, because the XML requests are just one of several ways through which requests can come in).

Example:

<request>
    <campaign>CAMP00001</campaign>
    <username>user_bob</username>
    <token>one-time-token-goes-here</token>
    ... more meta-data ...
    <records>
        <record id="90209">
            <name>John Doe</name>
            <address>Park Lane 191</address>
            <postal>99999</postal>
        </record>

        <record id="90210">
            <name>Jane Doe</name>
            <address>Park Lane 192</address>
            <postal>88888</postal>
        </record>
    </records>
</request>

Currently I'm validating by manually checking for the presence and validity of the content of the campaign, username and token fields. If possible, I'd like to do t开发者_开发技巧his using an XML schema so that it becomes easier to communicate to developers what meta-data they need to supply and in which formats - for campaigns, this is impossible as each campaign has its own set of fields and rules that are applied to those. Can such a thing be done?

(one solution I thought of is filling record with a set of <data> elements instead of named elements, and then have a very loose definition of <data> in the schema.. but that'd require changing the specs around)

You can use the Any type in a schema.

For Example

<xs:element name="foo">
    <xs:complexType>
        <xs:sequence>
            <xs:element name="first" type="xs:string"/>
            <xs:element name="second" type="xs:string"/>
            <xs:any minOccurs="0"/>
        </xs:sequence>
    </xs:complexType>
</xs:element>

This requires each foo element to have a first and second node and then allows any other elements as well. For example:

<foo>
    <first>Hello</first>
    <second>World</second>
    <other>can be anything</other>
    <nodes/>
</foo>

You could put the validated and unvalidated stuff in different namespaces and provide a pretty wide-open schema for the unvalidated content.