Bug 390669 [Accessibility]Press 'Tab' doesn't focus on the next report item when adding relative period aggregation.
xtab/org.eclipse.birt.report.item.crosstab.ui/src/org/eclipse/birt/report/item/crosstab/internal/ui/dialogs/CrosstabBindingDialogHelper.java
String arg = (String) iterator.next( );
				String value = getControlValue( paramsMap.get( arg ) );
				if ( value != null )
				{
					AggregationArgument argHandle = StructureFactory.createAggregationArgument( );
					argHandle.setName( arg );
					if ( ExpressionButtonUtil.getExpressionButton( paramsMap.get( arg ) ) != null )
					{
						ExpressionButtonUtil.saveExpressionButtonControl( paramsMap.get( arg ),
								argHandle,
								AggregationArgument.VALUE_MEMBER );
					}
					else
					{
						Expression expression = new Expression( value,
								ExpressionType.JAVASCRIPT );
						argHandle.setExpressionProperty( AggregationArgument.VALUE_MEMBER,
								expression );
					}
					binding.addArgument( argHandle );
				}
			}
		}
		else
		{
			for ( int i = 0; i < DATA_TYPE_CHOICES.length; i++ )
			{
				if ( DATA_TYPE_CHOICES[i].getDisplayName( )
						.equals( cmbType.getText( ) ) )
				{