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
* Returns the container element.
	 * <p>
	 * Part of: The containment system.
	 * 
	 * @return Returns the container.
	 */
	public DesignElement getContainer( )
	{
		return container;
	}
	/**
	 * Caches the child-to-container relationship. The caller must have
	 * validated that the relationship is valid.
	 * <p>
	 * Part of: The containment system.
	 * 
	 * @param obj
	 *            the container to set
	 * @param slot
	 *            the slot within the container where this element resides
	 */
	public void setContainer( DesignElement obj, int slot )
	{
		container = obj;
		containerSlotID = slot;
	}
	/**
	 * Gets the property data for either a system-defined or user-defined
	 * property.
	 * <p>