Bug 119566 Support template items in page header/footer
Currently you can't create template report items inside a page header/footer. This should be fixed.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
if ( derived == null )
			derived = new ArrayList( );
		assert child != null;
		assert child.getExtendsElement( ) == this;
		assert !derived.contains( child );
		assert child.getDefn( ) == getDefn( );
		derived.add( child );
	}
	/**
	 * Removes a cached element that derives from this element.
	 * <p>
	 * Part of: Inheritance system.
	 * 
	 * @param child
	 *            The old derived element.
	 */
	protected void dropDerived( DesignElement child )
	{
		assert derived != null;
		assert child != null;
		assert child.getExtendsElement( ) == this;
		assert derived.contains( child );
		derived.remove( child );
	}
	/**
	 * Sets the parent element. This version should be used to implement a
	 * command to change the parent element. The caller must have validated that
	 * the new parent is valid for this element.
	 * <p>
	 * Part of: Inheritance system.