(all) => {
  //put the file selection part in a closure, so that the list of all files is kept private.
  pages: {
    /*
    list is all the files in current directory.
    allfiles is all source files: ending with `.md` and not starting with `_`.
    pubfiles is the subset containing the string `_pub`.
    files selects either of these depending on the argument passed to this file.
    */
  //  allfiles: allfiles.sh() //reads MD files.
  //  pubfiles: pubfiles.sh(allfiles)
    (list): ..
    allfiles: Tree.filter(list, (val, key) => key.endsWith('.md') && !key.startsWith('_'))
    pubfiles: Tree.filter(allfiles, (val, key) => key.includes('_pub'))
    files: Tree.map( all ? allfiles : pubfiles, {value: (val) => Origami.document(val)})
    asHtml: Tree.map(files, (value) => Origami.mdHtml(value))
          → (values) => Tree.mapExtension(values, '.md→.html')

  /*
  after converting to html, we can extract a 'summary' from the file.
  With markdown, the title is taken from the YAML frontmatter,
  and ends up in a separate field of the document.
  So we dont have to worry about the title being part of the summary.
  */
  withSummary: Tree.map(asHtml, extractSummary.js)

  /*
  Removing private content coming below the html comment `<!--private-below-->`
  Only remove this if in public mode. So if this file is called as `site.ori("all")`,
  then final output is `withSummary`, otherwise it's `privateRemoved`.
  */
  privateRemoved: Tree.map(withSummary, removePrivate.js)
  final: (all ? withSummary : privateRemoved)
  
  }.final

  renderedPages: Tree.map(pages, page.ori)

  /*
  assets are relative to the pubfiles directory
  */
  css

  /*
  Now, I think I have enough to build both the individual pages and the index page!
  */
  index.html: indexPage.ori(pages)
  ...renderedPages/
}