Creates a new slide from XML.
        
        :return     <XWalkthroughSlide>

def fromXml(xml):
        """
        Creates a new slide from XML.
        
        :return     <XWalkthroughSlide>
        """
        slide = XWalkthroughSlide(**xml.attrib)
        
        # create the items
        for xgraphic in xml:
            slide.addItem(XWalkthroughItem.fromXml(xgraphic))
        
        return slide