title: Which attribute in XSD will annotate a field with @XmlElement(required = false) in JAXB generated classes
body: <p>I want to annotate a field in my jaxb generated class with this annotation - @XmlElement(required = false). Which attribute in the XSD would generate my field with this annotation?. 
  I can't hand type this as the JAXB classes are auto generated using Maven every time a build is run.</p>
  
  <p>My jaxb version is xjc 2.2.4-2</p>
  
  <p>Thanks</p>