sh the C++ compiler hard to
  its knees. For example, current compilers have a limit on recursion depth that
  may not be exceeded. Don't even think about writing a full pascal grammar using
  subrules alone. A grammar using subrules is a single C++ expression. Current
  C++ compilers cannot handle very complex expressions very well. Finally, a plain
  rule is still needed to act as place holder for subrules.</p>
<p>The code above is a good example of the recommended way to use subrules. Notice 
  the hiera