Defining a text template () node of a complex blended element

This question is related to that one. But somewhat advanced.

Let's assume we have xml:

<field name="test_field_0">
    Some text that is texty text.
    <subfield>Some text.</subfield>
</field>

      

        
        
        
      

    

Schematic for it from the linked question :

<xs:element name="field">
    <xs:complexType mixed="true">
        <xs:sequence>
                <xs:element ref="subfield" minOccurs="0" maxOccurs="unbounded" />
        </xs:sequence>
        <xs:attribute name="name" type="xs:string" />
    </xs:complexType>
</xs:element>

      

        
        
        
      

    

Now an additional requirement is that the element's text()

node field

must be governed by some pattern, for example:\p{Lu}(\p{Ll}\p{P}\p{Z})+