(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.

    NOTES:

    - if markdown files are empty, Origami.document() will error.
    */

    /*
      this is the external filename method. 
    */
  //  allfiles: allfiles.sh() //reads MD files.
  //  pubfiles: pubfiles.sh(allfiles)
    (list): ..
    allfiles: Tree.filter(list, (val, key) => key.endsWith('.md') && !key.startsWith('_'))
      → (items) => Tree.map(items, {value: (value) => Origami.document(value)}) //if I don't use the verbose syntax I get the filename characters as part of value!
      → (items) => Tree.map(items, { value: (value, key) => addFilenameData.js(value, key)})

    pubfiles: Tree.filter(allfiles, (val, key) => val.fnd.tags?.includes('pub'))

    /*
      Now convert to html.
    */
    asHtml: Tree.map(all ? allfiles: pubfiles, {
      value: (value) => Origami.mdHtml(value)
      key: (value, key) => `${value.fnd.name}.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) => <page.ori>(page, all))
  /*
  the rendered pages contain links and images.
  We want to find those, and insert a tree of their maps into the output.
  First test is whether that works.
  Second test is whether the paths will be correct.
  */
  hast = Tree.map(renderedPages, parseHtml.js)
  links:  Tree.flat(hast, 2) → (a) => [...new Set(a)]

  /*
  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, all)
  ...renderedPages/
}