restrict element content by the attribute from a different namespace?

Perhaps I'm looking into a wrong direction and this is totally wrong, 

but I would like restrict element content by the attribute from a different
namespace.

 

Suppose I have a schema "base.xsd" where declared a set of attributes, for
say:

<!-- base.xsd -->

<xs:attribute name="readonly" type="xs:boolean" />

....

this is used for service information.

 

In the schema "main.xsd" I have set of elements:

<!-- main.xsd -->

<xs:element name="generic" type="xs:anyType" abstract="1" />

<xs:element name="field1"  type="xs:string"  substitutionGroup="generic"
base:readonly="0" />

<xs:element name="field2"  type="xs:string"  substitutionGroup="generic"
base:readonly="1" />

....

<xs:element name="fields">

      <xs:complexType>

            <xs:sequence>

                  <xs:element ref="generic" minOccurs="1"
maxOccurs="unbounded" />

            </xs:sequence>

      </xs:complexType>

</xs:element>

 

As you can see abstract types and elements in play, that's solely for
versioning, all those C#/java tends to 

tolerate following construct more loose and adding new field generally
doesn't break the code.

What I would like to do, is restrict set of elements in the <fields> to only
where base:readonly="1"