Bug 161174 Expect to set/get interval range with a 'String' param in GroupHandle.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/GroupHandle.java
*/
	public void setKeyExpr( String expr ) throws SemanticException
	{
		setProperty( GroupElement.KEY_EXPR_PROP, expr );
	}
	/**
	 * Returns the iterator for Sort list defined on the group. The element in
	 * the iterator is the corresponding <code>StructureHandle</code>.
	 * 
	 * @return the iterator for <code>SortKey</code> structure list defined on
	 *         the group.
	 */
	public Iterator sortsIterator( )
	{
		PropertyHandle propHandle = getPropertyHandle( GroupElement.SORT_PROP );
		assert propHandle != null;
		return propHandle.iterator( );
	}
	/**
	 * Returns an iterator for the filter list defined on the group. Each object
	 * returned is of type <code>StructureHandle</code>.
	 * 
	 * @return the iterator for <code>FilterCond</code> structure list defined
	 *         on the group.
	 */
	public Iterator filtersIterator( )
	{
		PropertyHandle propHandle = getPropertyHandle( GroupElement.FILTER_PROP );
		assert propHandle != null;
		return propHandle.iterator( );