http://www.w3.org/1999/xhtml
group heading

Model

>
(h1 | h2 | h3 | h4 | h5 | h6)

Source

<xs:group name="heading">
  <xs:choice>
    <xs:element ref="h1"/>
    <xs:element ref="h2"/>
    <xs:element ref="h3"/>
    <xs:element ref="h4"/>
    <xs:element ref="h5"/>
    <xs:element ref="h6"/>
  </xs:choice>
</xs:group>