There are other codes on russian books:
УДК = Universal Decimal Classification (UDC), example: УДК 821.111(73)
ББК = Library bibliographic classification, example: ББК 84(7Сое)
Author's sign, example: Б48
Please, add it to the list!
Moreover UDC is international classifier. There is the non-profit UDC Consortium, which moderates it. This identifier is a must have here.
ББК is a USSR analogue of UDC. Nowadays it's actively used in Russia, only recently discontinued in Ukraine. Not sure about the other post USSR countries. And still - this is a huge amount of books covered and thus a must have here.
Please don't ignore this.
+1 add this the support of these codes ASAP
The correct link to BBK
Sorry for excessive message, the last bracket is a part of the link