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.