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 a list of property definitions
	 */
	public List getPropertyDefns( )
	{
		List list = getDefn( ).getProperties( );
		DesignElement e = this;
		while ( e != null )
		{
			if ( e.userProperties != null )
				list.addAll( e.userProperties.values( ) );
			e = e.getExtendsElement( );
		}
		return list;
	}
	/**
	 * Returns the internal name of the element. This name matches the name of
	 * the definition for the element.
	 * 
	 * @return the internal element type name for this element
	 */
	public abstract String getElementName( );
	/*
	 * (non-Javadoc)
	 * 
	 * @see java.lang.Object#equals(java.lang.Object)
	 */
	public boolean equals( Object obj )
	{
		if ( obj == null )