XSElement libraryElement = elements[0];
XSIdentityConstraint[] ics = libraryElement.getIdentityConstraints();
assertEquals( 1, ics.length );
XSIdentityConstraint ic = ics[0];
assertEquals( "book-key", ic.getName() );
XSElementOrAttrRef[][] icMatchCriteria = ic.getMatchCriteria();
assertEquals( 2, icMatchCriteria.length );
assertEquals( 1, icMatchCriteria[0].length );
assertEquals( 1, icMatchCriteria[1].length );