Parse a <screenshot> object

def _parse_tree(self, node):
        """ Parse a <screenshot> object """
        if 'type' in node.attrib:
            self.kind = node.attrib['type']
        for c3 in node:
            if c3.tag == 'caption':
                self.caption = _parse_desc(c3)
            elif c3.tag == 'image':
                im = Image()
                im._parse_tree(c3)
                self.add_image(im)