/! composite block
- @parts.each do |part|
  - template = part.slug.gsub(/[^a-z0-9_]/, '_').downcase.to_sym
  /! slug: #{part.slug}, template: #{template}
  - if template.in?(CompositeCell::SPECIFIC_CELLS)
    = render_cell :composite, template, structure: part, root_structure: @root
  - else
    = render_cell :composite, :page, template, structure: part, root_structure: @root
/! end composite block