Bug 138562 Splite extendsexcpetion to seperate sub class
The suggestion is Parent invalid Cycle extends Different type extends Not top level extends
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
if ( content == null || content.getContainer( ) != this )
			return NO_SLOT;
		return content.getContainerSlot( );
	}
	/**
	 * Checks whether the property of current element is editable.
	 * 
	 * @return <code>true</code> if the property of current element is
	 *         editable. Otherwise <code>false</code>.
	 */
	public boolean canEdit( )
	{
		return !isRootIncludedByModule( );
	}
	/**
	 * Determines if this element can be dropped from its container.
	 * 
	 * @return <code>true</code> if it can be dropped. Returns
	 *         <code>false</code> otherwise.
	 */
	public boolean canDrop( )
	{
		
		
		if ( isRootIncludedByModule( ) )
			return false;
		
		
		if ( isVirtualElement( ) )
			return false;