public boolean blockExtension()
True if extension is blocked.

 public boolean blockRestriction()
True if restriction is blocked.

 public boolean blockSubstitution()
True if element substitution is blocked.

 public SchemaIdentityConstraint[] getIdentityConstraints()
Returns all the Key, KeyRef, and Unique constraints
on this element.

 public boolean isAbstract()
True if this element is prohibited in content. Only
sensible if this is the head of a substitution group;
then only substitution group members can appear.


Although local elements cannot be abstract, if an element 
use is a ref to a global element, then the flag from the 
global element is copied in to the local element where the 
use occurs.