Search node's entire subtree for a match.
Overuse of this may degrade analyzer performance.
Note that "t" is short for "trigger", not "tree".
# If a node labeled _det is followed by a node with a thousand child
nodes, that subtree
# will be searched for a node with a _noun label. So tree can be costly and wildly inaccurate,
# and must be used with caution.
_np <- _det _noun [tree] @@
singlet, Phrase Element Modifiers.