Apparently this function DOES, in fact, return a value as many of the MING examples show. It is a SWFDisplayItem.  Here is an excerpt of an example that appears elsewhere in the MING docs...
<?php
  $p = new SWFSprite();
  $i = $p->add($s);
  $p->nextFrame();
  $i->rotate(15);
  $p->nextFrame();
?>
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