def as_xml(self):
        """XML representation of the error to be used in HTTP response.

        This XML format follows the IIIF Image API v1.0 specification,
        see <http://iiif.io/api/image/1.0/#error>
        """
        # Build tree
        spacing = ("\n" if (self.pretty_xml) else "")
        root = Element('error', {'xmlns': I3F_NS})
        root.text = spacing
        e_parameter = Element('parameter', {})
        e_parameter.text = self.parameter
        e_parameter.tail = spacing
        root.append(e_parameter)
        if (self.text):
            e_text = Element('text', {})
            e_text.text = self.text
            e_text.tail = spacing
            root.append(e_text)
        # Write out as XML document to return
        tree = ElementTree(root)
        xml_buf = io.BytesIO()
        if (sys.version_info < (2, 7)):
            tree.write(xml_buf, encoding='UTF-8')
        else:
            tree.write(xml_buf, encoding='UTF-8',
                       xml_declaration=True, method='xml')
        return(xml_buf.getvalue().decode('utf-8'))
XML representation of the error to be used in HTTP response.

        This XML format follows the IIIF Image API v1.0 specification,
        see <http://iiif.io/api/image/1.0/#error>