 by modifiers (such as modifiers and prepositions), etc.
"ARG2" represents an object of verbs, prepositions, etc.  The other
"ARGx" represents objects and complements of verbs, etc.  "MOD" is
used for participial constructions etc.  It denotes a clause modified
by another clause, such as a verbal or an adverbial clause, and the
subordinate clause has its own ARG1.

<p>
A predicate word is not always a head word.  In the above example, The
head word for "an efficient HPSG parser" is "parser" but "parser" is
