[O] Access outline from a code block

[Rob Duncan]

The manual states that the :var header argument can be given a reference to a 
table, a list, a literal example, a code block, or results.  But I want to use 
a reference to an outline tree—is there some way to do this?  My experiments 
have all failed:

#+NAME: example-outline
* L1
** L2a
*** L3a
** L2b
** L2c

* Results
#+NAME: table-length
#+BEGIN_SRC emacs-lisp :var ref=example-outline
(print (format "%S" ref))
  #+END_SRC

#+RESULTS: table-length
: "nil"

Alternatively, is there a way to pass the name as a literal and then explicitly 
resolve it within the code block and get the outline data?

Thanks,

Rob.