# File lib/asciidoctor/converter/docbook45.rb, line 55
    def author_element doc, index = nil
      firstname_key = index ? %(firstname_#{index}) : 'firstname'
      middlename_key = index ? %(middlename_#{index}) : 'middlename'
      lastname_key = index ? %(lastname_#{index}) : 'lastname'
      email_key = index ? %(email_#{index}) : 'email'

      result = []
      result << '<author>'
      result << %(<firstname>#{doc.attr firstname_key}</firstname>) if doc.attr? firstname_key
      result << %(<othername>#{doc.attr middlename_key}</othername>) if doc.attr? middlename_key
      result << %(<surname>#{doc.attr lastname_key}</surname>) if doc.attr? lastname_key
      result << %(<email>#{doc.attr email_key}</email>) if doc.attr? email_key
      result << '</author>'

      result * EOL
    end