e wrapper element declaration to be required.

 <p>
 If required() is true, then the corresponding generated
 XML schema element declaration will have <code>minOccurs="1"</code>,
 to indicate that the wrapper element is always expected.

 <p>
 Note that this only affects the schema generation, and
 not the unmarshalling or marshalling capability. This is
 simply a mechanism to let users express their application constraints
 better.</div>
<dl>
<dt><span class="simpleTagLabel">Since:</span></dt>
<dd>1.6, JAX