Rename the numth context node to name. If num is absent or 0, rename last context node.
xrename(name [,num])
@PATH _ROOT _sentence _segment
# This rule says that if a _noun is the last
# node of a _segment, rename _segment to _np.
@POST
xrename("_np",3);
@RULES
_xNIL <- _noun [s] _xEND @@