Node visitor interface for traversing a .spec tree
--++ Object Method startVisit($node) -> $boolean
Called on each node in the tree as a visit starts.
Return 1 to continue the visit, or 0 to terminate it.
--++ Object Method endVisit($node) -> $boolean
Called on each node in the tree as a visit finishes.
Return 1 to continue the visit, or 0 to terminate it.