Bug 151959 inappropriate screen operation
steps to reproduce: - create a report - add a grid item (3x3) - switch to Outline view - expand the grid item to see its rows and cells - select the grid item, and drag it into any of its own cell expected behavior: - is it an invalid screen operation? if it is, it should be banned actual behavior: - the grid item was disappeared surprisingly
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
{
		int slotCount = getDefn( ).getSlotCount( );
		if ( slotCount == 0 )
			return;
		slots = new ContainerSlot[slotCount];
		for ( int i = 0; i < slotCount; i++ )
		{
			SlotDefn slot = (SlotDefn) getDefn( ).getSlot( i );
			if ( slot.isMultipleCardinality( ) )
				slots[i] = new MultiElementSlot( );
			else
				slots[i] = new SingleElementSlot( );
		}
	}
	/**
	 * Returns the validation error list, each of which is the instance of
	 * <code>SemanticExcpetion</code>.
	 * 
	 * @return the validation error list.
	 */
	public List getErrors( )
	{
		if ( errors == null )
			return new ArrayList( );
		return errors;
	}
	/**
	 * Returns the identifier for locating element to user. This identifier
	 * string helps user locate this element in user interface. If this element
	 * has name defined, the name and element type are returned with the form