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
* @param content
	 *            the target element to be inserted
	 * @return a list containing exceptions.
	 */
	protected List checkContent( Module module, DesignElement container,
			int slotId, DesignElement content )
	{
		return new ArrayList( );
	}
	/**
	 * Checks whether elements with the given element definition can be inserted
	 * to the slot <code>slotId</code> in another element
	 * <code>container</code>.
	 * 
	 * @param module
	 *            the module
	 * @param container
	 *            the container element
	 * @param slotId
	 *            the slot id of the container element
	 * @param defn
	 *            the element definition
	 * @return a list containing exceptions.
	 */
	protected List checkContent( Module module, DesignElement container,
			int slotId, IElementDefn defn )
	{
		return new ArrayList( );
	}
	/**