extension 

A unique document identifier managed internally by the 
organization specified in 'root'. Can be any alpha-numeric 
format desired by the organization. (ex: "hml-0.9.7-123456789.23a")
(required and must be at least 1 non-whitespace character long and 
guarantee uniqueness)

Simple Type Information

Used By

Attribute hmlid/@extension

Source 

<xs:simpleType name="extension">
  <xs:annotation>
    <xs:documentation>A unique document identifier managed internally by the organization specified in 'root'. Can be any alpha-numeric format desired by the organization. (ex: "hml-0.9.7-123456789.23a") (required and must be at least 1 non-whitespace character long and guarantee uniqueness)</xs:documentation>
  </xs:annotation>
  <xs:restriction base="xs:string">
    <xs:minLength value="1"/>
  </xs:restriction>
</xs:simpleType>