** eval and noeval
   :PROPERTIES:
   :DATE:     2010-08-26
   :END:
date, should export both, but won't output results because of presence
of the =:noeval= header argument.
#+begin_src sh :noeval :exports both
  date
#+end_src

should export code, so no need to do anything
#+begin_src sh
  date
#+end_src

should export nothing, and should not query
#+name: this-is-ls
#+begin_src sh :eval query :exports code
  date
#+end_src

should export results, and should trigger query above
#+begin_src emacs-lisp :var ls=this-is-ls :exports results
  ls
#+end_src