dx:usage 

Comment describing your root element

Element Information

Model

dx:name , dx:occurance , dx:introduction , dx:body{0,1} , (dx:constraint*)
Children: dx:body, dx:constraint, dx:introduction, dx:name, dx:occurance

Attributes

QName Type Fixed Default Use Inheritable Annotation
dx:href xs:string optional 
To provide a link to the element definition in case the inforamtion is coming from an external file.
The link would correpsond to a xlink.

Used By

Complex Types dx:elementType, dx:valueType
Elements dx:element, dx:occurance

Source 

<xs:element name="usage">
  <xs:annotation>
    <xs:documentation>Comment describing your root element</xs:documentation>
  </xs:annotation>
  <xs:complexType>
    <xs:sequence>
      <xs:element ref="dx:name"/>
      <xs:element ref="dx:occurance">
        <xs:annotation>
          <xs:documentation>cardinality is mandatory for the generic usage. It may be present more than once in case it changes for different usages, implementations or targets</xs:documentation>
        </xs:annotation>
      </xs:element>
      <xs:element ref="dx:introduction"/>
      <xs:element ref="dx:body" minOccurs="0">
        <xs:annotation>
          <xs:documentation>cardinality is mandatory for the generic usage. It may be present more than once in case it changes for different usages, implementations or targets</xs:documentation>
        </xs:annotation>
      </xs:element>
      <xs:choice minOccurs="0" maxOccurs="unbounded">
        <xs:element ref="dx:constraint" minOccurs="0" maxOccurs="unbounded"/>
      </xs:choice>
    </xs:sequence>
    <xs:attribute ref="dx:href"/>
  </xs:complexType>
</xs:element>

Sample