code: func prefixesListing(pfx string, prefixes []string) []listingItem {
  	out := make([]listingItem, 0, len(prefixes)+1)
  	if pfx != "" {
  		parent := ""
  		if idx := strings.LastIndex(pfx, "/"); idx != -1 {
  			parent = pfx[:idx]
  		}
  		out = append(out, listingItem{
  			Back: true,
  			Href: prefixPageURL(parent),
  		})
  	}
  	return pathListing(pfx, prefixes, out, func(p string) listingItem {
  		return listingItem{
  			Href: prefixPageURL(p),
  		}
  	})
  }
docs: // prefixesListing formats a list of child prefixes of 'pfx'.
  //
  // The result includes '..' if 'pfx' is not root.