xl:useEnum 

Enumerated values for the use attribute on extended link arcs.

Simple Type Information

Used By

Attribute xl:arcType/@use

Source 

<simpleType name="useEnum">
  <annotation>
    <documentation>Enumerated values for the use attribute on extended link arcs.</documentation>
  </annotation>
  <restriction base="NMTOKEN">
    <enumeration value="optional"/>
    <enumeration value="prohibited"/>
  </restriction>
</simpleType>