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
lblParam.setLayoutData( gd );
	}
	/**
	 * Creates the Period control part of an argument info.
	 * 
	 * @param name
	 *            The name of the argument info
	 * @param types
	 *            The period types
	 * @param numColumns
	 *            Number of columns the control takes
	 */
	private void createPeriodPart( final String name, List<Period_Type> types,
			int numColumns )
	{
		if ( types != null && types.size( ) > 0 )
		{
			final Combo cmbDataField = new Combo( calculationComposite,
					SWT.BORDER | SWT.READ_ONLY );
			cmbDataField.setLayoutData( GridDataFactory.fillDefaults( )
					.grab( true, false )
					.span( numColumns, 1 )
					.create( ) );
			cmbDataField.setVisibleItemCount( 30 );
			initCalculationDataFields( cmbDataField, name, types );
			cmbDataField.addModifyListener( new ModifyListener( ) {
				public void modifyText( ModifyEvent e )
				{
					modifyDialogContent( );
					validate( );