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
* 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 )
			return false;
		if ( obj == this )
			return true;
		if ( obj instanceof DesignElementHandle )
			return ( (DesignElementHandle) obj ).getElement( ) == this;
		return false;
	}
	/**
	 * Returns the slot that contains the given content element.
	 * 
	 * @param content
	 *            the element to find
	 * @return the number of the slot that contains the element, or -1 if this
	 *         element does not contain the content element.
	 */
	public int findSlotOf( DesignElement content )
	{