bson_iter_document(3) on Linux
The text 068582a48e3b, as Debian 9 (Stretch) shipped it.
The bson_iter_document() function shall retrieve the raw buffer of a sub-document from iter. iter MUST be on an element that is of type BSON_TYPE_DOCUMENT. This can be verified with bson_iter_type() or the BSON_ITER_HOLDS_DOCUMENT() macro.