http://www.w3.org/1999/xhtml
simpleType tabindexNumber

Super Types

{http://www.w3.org/2001/XMLSchema}nonNegativeInteger
  |
  +--{http://www.w3.org/1999/xhtml}Number (restriction)
       |
       +--{http://www.w3.org/1999/xhtml}tabindexNumber (restriction)

Documentation

      tabindex attribute specifies the position of the current element
      in the tabbing order for the current document. This value must be
      a number between 0 and 32767. User agents should ignore leading zeros. 
      

Source

<xs:simpleType name="tabindexNumber">
  <xs:restriction base="Number">
    <xs:minInclusive value="0"/>
    <xs:maxInclusive value="32767"/>
  </xs:restriction>
</xs:simpleType>