Sets iter to be the child of parent, using the given index.
The first index is 0. If n is too big, or parent has no children,
iter is set to an invalid iterator and FALSE is returned. parent
will remain a valid node after this function has been called. As a
special case, if parent is NULL, then the nth root node
is set.
Sets iter to be the child of parent, using the given index. The first index is 0. If n is too big, or parent has no children, iter is set to an invalid iterator and FALSE is returned. parent will remain a valid node after this function has been called. As a special case, if parent is NULL, then the nth root node is set.