bool bson_iter_find_descendant (bson_iter_t *iter, const char *dotkey, bson_iter_t *descendant);
The bson_iter_find_descendant() function shall follow standard MongoDB dot notation to recurse into subdocuments. descendant will be initialized and advanced to the descendant. If false is returned, both iter and descendant should be considered invalid.
true is returned if the requested key was found. If not, false is returned and iter was exhausted and should now be considered invalid.