Restrictions on how ASD grammars should be written to be used with ASDParser:

• Dummy nodes in the grammar should never be initial nodes.  The parser will only use initial nodes in the grammar that correspond to actual words in the given utterance.
• For each initial node in the grammar, there should be at least one final node reachable from it.  Otherwise, the parses starting at that initial node can't possibly succeed.
• Since dummy (null) nodes in the grammar don't match any words in the utterance being parsed, there must not be cycles of dummy nodes in the grammar.  Otherwise the parser can get into an unending loop in such a cycle.