bson_iter_init(3) on Linux
The text bb55250cb09e, as Debian 9 (Stretch) shipped it.
The bson_iter_init() function shall initialize iter to iterate upon the BSON document bson. Upon initialization, iter is placed before the first element. Callers must call bson_iter_next(), bson_iter_find(), or bson_iter_find_case() to advance to an element.