MDAC 2.5 SDK - ODBC Programmer's Reference
Chapter 11: Retrieving Results (Advanced)
Because bookmarks are byte-comparable, they can be compared for equality or inequality. To do so, an application treats each bookmark as an array of bytes and compares two bookmarks byte-by-byte. Because bookmarks are guaranteed to be distinct only within a result set, it makes no sense to compare bookmarks that were obtained from different result sets.