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
implements
			IDesignElement,
			IPropertySet,
			IDesignElementModel
{
	/**
	 * Constant indicate that the element has no virtual parent.
	 */
	public final static long NO_BASE_ID = -1;
	/**
	 * Constant indicate that the element has no id.
	 */
	public final static long NO_ID = 0;
	/**
	 * The max length the display label for every element. If the length exceeds
	 * this limit, the exceeding part will be shown as "...".
	 */
	private static final int MAX_DISPLAY_LABEL_LEN = 30;
	/**
	 * Elements have an optional name. The name may be required by some element
	 * types. If so, the derived element class should enforce the use of the
	 * name. The name is non-localizable.
	 * <p>
	 * The name often occurs in a name space. Derived classes must enforce the
	 * name space rules. This class simply maintains the name itself.
	 */
	protected String name = null;
	/**