elml:preReqItem 

Each element preReqItem defines one prerequisite.

Element Information

Model

Attributes

QName Type Fixed Default Use Inheritable Annotation
label xs:string required
priority elml:ScaleType optional 
The attribute priority defines the priority (low, medium, high) by which the mentioned lesson must be studied before attempting the current lesson.

Source 

<xs:element name="preReqItem" maxOccurs="unbounded">
  <xs:annotation>
    <xs:documentation>Each element preReqItem defines one prerequisite.</xs:documentation>
  </xs:annotation>
  <xs:complexType>
    <xs:simpleContent>
      <xs:extension base="xs:string">
        <xs:attributeGroup ref="elml:LessonLabelReq"/>
        <xs:attributeGroup ref="elml:PriorityImp"/>
      </xs:extension>
    </xs:simpleContent>
  </xs:complexType>
</xs:element>

Sample