drupal/modules/help/help.module

<?php
// $Id$

function help_system($field){
  $system["description"] = t("Manages displaying online help.");
  return $system[$field];
}

function help_link($type) {
  if ($type == "admin") {
    $links[] = la(t("help"), array("mod" => "help"));
  }

  return $links ? $links : array();
}

function help_admin() {

  foreach (module_list() as $name) {
    if (module_hook($name, "help")) {
      $links[] = la($name, array("mod" => "help"), $name);
    }
  }

  print "<small>". implode(" | ", $links) ."</small><hr />";

  foreach (module_list() as $name) {
    if (module_hook($name, "help")) {
      print "<h2><a name=\"$name\">". ucfirst($name) ." module</a></h2>";
      print module_invoke($name, "help");
    }
  }
}

?>