Liquid helium (and other similar fluids) can "climb up" the walls of their containers. Who does the work in this case, and what kind of energy does it use? I'm sure we can't make a perpetuum mobile out of this, so I guess some kind of energy must somehow be expended to make the fluid "climb up" the wall.


Question: How do I add to $page_top in html.tpl.php?
Answer: Have a look at how the Drupal core toolbar module does this:

/**
 * Implements hook_page_build().
 *
 * Add admin toolbar to the page_top region automatically.
 */
function toolbar_page_build(&amp;$page) {
  $page['page_top']['toolbar'] = array(
    '#pre_render' =&gt; array('toolbar_pre_render'),
    '#access' =&gt; user_access('access toolbar'),
    'toolbar_drawer' =&gt; array(),
  );
}


This is probably the most correct way of adding something to the page top as you can comfortably use render arrays.