Odoc 2.x had a different way to specify the hierarchy of the output pages. This still works, though it is deprecated. Documentation for the feature may be found here.
odoc
odoc.document
odoc.examples
odoc.html
odoc.html_support_files
odoc.index
odoc.json_index
odoc.latex
odoc.loader
odoc.manpage
odoc.model
odoc.model_desc
odoc.ocamlary
odoc.occurrences
odoc.odoc
odoc.odoc_utils
odoc.search
odoc.search_html_frontend
odoc.syntax_highlighter
odoc.xref2
odoc.xref_test