the order in which nodes are visited - G_IN_ORDER, G_PRE_ORDER, G_POST_ORDER, or G_LEVEL_ORDER
which types of children are to be searched, one of G_TRAVERSE_ALL, G_TRAVERSE_LEAVES and G_TRAVERSE_NON_LEAVES
the data to find
the found GNode, or NULL if the data is not found
Finds a GNode in a tree.