def METHOD_NAME(self, comment_data):
    # Write the <authors> element.
    author_count = 0
    self._xml_start_tag('authors')
    for comment in comment_data:
        author = comment[3]
        if author is not None and author not in self.author_ids:
            # Store the author id.
            self.author_ids[author] = author_count
            author_count += 1
            # Write the author element.
            self._write_author(author)
    self._xml_end_tag('authors')