/ this made tests crash so I replaced it with asciidoctor-backends HTML5 slim template
/- if @document.attr? :toc
/  - toc_id = @id
/  - toc_role = (attr 'role', (@document.attr 'toc-class', 'toc'))
/  - toc_title_id = nil
/  - toc_title = title? ? title : (@document.attr 'toc-title')
/  - toc_levels = (attr? :levels) ? (attr :levels).to_i : (@document.attr :toclevels, 2).to_i
/  - if !toc_id && (@document.embedded? || !(@document.attr? 'toc-placement'))
/    - toc_id = 'toc'
/    - toc_title_id = 'toctitle'
/  div id=toc_id class=toc_role
/    .title id=toc_title_id =toc_title
/    =Asciidoctor::HTML5::DocumentTemplate.outline(@document, toc_levels)
#toc class=(document.attr 'toc-class', 'toc')
  #toctitle =(document.attr 'toc-title')
  / Renders block_outline.html.
  = converter.convert document, 'outline'