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
* @return the list of the errors found in validation, each of which is the
	 *         <code>SemanticException</code> object.
	 */
	protected List validateStructureList( Module module, String propName )
	{
		return StructureListValidator.getInstance( ).validate( module, this,
				propName );
	}
	/**
	 * Checks all structures in the specific property whose type is structure
	 * list property type. This method is used in command. If any error is
	 * found, the exception will be thrown.
	 * 
	 * @param module
	 *            the module
	 * @param propDefn
	 *            the property definition of the list property
	 * @param list
	 *            the structure list to check
	 * @param toAdd
	 *            the structure to add. This parameter maybe is
	 *            <code>null</code>.
	 * @throws PropertyValueException
	 *             if the structure list or the structure to add has any
	 *             semantic error..
	 */
	public void checkStructureList( Module module, PropertyDefn propDefn,
			List list, IStructure toAdd ) throws PropertyValueException
	{
		List errorList = StructureListValidator.getInstance( )