Node attributes to be printed. Can be either a character (i.e. the name of a Node field),
a Node method, or a function taking a Node as a single argument. See Get for details on
the meaning of attribute.
pruneMethod
The method used to prune for printing. If NULL, the entire tree is displayed. If
"simple", then only the first limit nodes are displayed. If "dist", then Nodes are removed
everywhere in the tree, according to their level.
limit
The maximum number of nodes to print. Can be NULL if the
entire tree should be printed.