class Asciidoctor::Parser

def self.parse_manpage_header(reader, document, block_attributes)
  if ManpageTitleVolnumRx =~ (doc_attrs = document.attributes)['doctitle']
    doc_attrs['manvolnum'] = manvolnum = $2
    doc_attrs['mantitle'] = (((mantitle = $1).include? ATTR_REF_HEAD) ? (document.sub_attributes mantitle) : mantitle).downcase
  else
    logger.error message_with_context 'non-conforming manpage title', source_location: (reader.cursor_at_line 1)
    # provide sensible fallbacks
    doc_attrs['mantitle'] = doc_attrs['doctitle'] || doc_attrs['docname'] || 'command'
    doc_attrs['manvolnum'] = manvolnum = '1'
  end
  if (manname = doc_attrs['manname']) && doc_attrs['manpurpose']
    doc_attrs['manname-title'] ||= 'Name'
    doc_attrs['mannames'] = [manname]
    if document.backend == 'manpage'
      doc_attrs['docname'] = manname
      doc_attrs['outfilesuffix'] = %(.#{manvolnum})
    end
  else
    reader.skip_blank_lines
    reader.save
    block_attributes.update parse_block_metadata_lines reader, document
    if (name_section_level = is_next_line_section? reader, {})
      if name_section_level == 1
        name_section = initialize_section reader, document, {}
        name_section_buffer = (reader.read_lines_until break_on_blank_lines: true, skip_line_comments: true).map {|l| l.lstrip }.join ' '
        if ManpageNamePurposeRx =~ name_section_buffer
          doc_attrs['manname-title'] ||= name_section.title
          doc_attrs['manname-id'] = name_section.id if name_section.id
          doc_attrs['manpurpose'] = $2
          if (manname = $1).include? ATTR_REF_HEAD
            manname = document.sub_attributes manname
          end
          if manname.include? ','
            manname = (mannames = (manname.split ',').map {|n| n.lstrip })[0]
          else
            mannames = [manname]
          end
          doc_attrs['manname'] = manname
          doc_attrs['mannames'] = mannames
          if document.backend == 'manpage'
            doc_attrs['docname'] = manname
            doc_attrs['outfilesuffix'] = %(.#{manvolnum})
          end
        else
          error_msg = 'non-conforming name section body'
        end
      else
        error_msg = 'name section must be at level 1'
      end
    else
      error_msg = 'name section expected'
    end
    if error_msg
      reader.restore_save
      logger.error message_with_context error_msg, source_location: reader.cursor
      doc_attrs['manname'] = manname = doc_attrs['docname'] || 'command'
      doc_attrs['mannames'] = [manname]
      if document.backend == 'manpage'
        doc_attrs['docname'] = manname
        doc_attrs['outfilesuffix'] = %(.#{manvolnum})
      end
    else
      reader.discard_save
    end
  end
  nil
end