is-a 

When a pattern element has the attribute is-a with a value specifying
the name of an abstract pattern, then the pattern is an instance of an abstract pattern.

Attribute Information

Used By

Element sch:pattern

Source 

<xs:attribute name="is-a" type="xs:IDREF">
  <xs:annotation>
    <xs:documentation>When a pattern element has the attribute is-a with a value specifying the name of an abstract pattern, then the pattern is an instance of an abstract pattern.</xs:documentation>
  </xs:annotation>
</xs:attribute>

Sample