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
* Part of: Property system and user-defined property system
	 * 
	 * @param propName
	 *            The name of the property to lookup.
	 * @return The property definition, or null, if the property is undefined.
	 */
	public ElementPropertyDefn getPropertyDefn( String propName )
	{
		
		ElementPropertyDefn prop = (ElementPropertyDefn) getDefn( )
				.getProperty( propName );
		if ( prop == null )
			prop = getUserPropertyDefn( propName );
		return prop;
	}
	/**
	 * Validates that the given property name is either a system-defined or
	 * user-defined property.
	 * <p>
	 * Part of: Property system.
	 * 
	 * @param propName
	 *            The name of the property to validate.
	 * @throws PropertyNameException
	 *             If the property is undefined.
	 */
	void validatePropertyName( String propName ) throws PropertyNameException
	{
		if ( getPropertyDefn( propName ) == null )
			throw new PropertyNameException( this, propName );