Add header line, updating any necessary support indices

        :return: ``False`` on conflicting line and ``True`` otherwise

def add_line(self, header_line):
        """Add header line, updating any necessary support indices

        :return: ``False`` on conflicting line and ``True`` otherwise
        """
        self.lines.append(header_line)
        self._indices.setdefault(header_line.key, OrderedDict())
        if not hasattr(header_line, "mapping"):
            return False  # no registration required
        if self.has_header_line(header_line.key, header_line.mapping["ID"]):
            warnings.warn(
                (
                    "Detected duplicate header line with type {} and ID {}. "
                    "Ignoring this and subsequent one"
                ).format(header_line.key, header_line.mapping["ID"]),
                DuplicateHeaderLineWarning,
            )
            return False
        else:
            self._indices[header_line.key][header_line.mapping["ID"]] = header_line
            return True