-However, document is lacking real specification, so tag decoding
-was done to be compliant with 3M implementation
+L<http://solutions.3m.com/wps/portal/3M/en_US/3MLibrarySystems/Home/Resources/CaseStudiesAndWhitePapers/RFID501/>
+
+Goal is to be compatibile with existing 3M Alphanumeric tag format
+which, as far as I know, isn't specificed anywhere. My documentation about
+this format is available at
+
+L<http://saturn.ffzg.hr/rot13/index.cgi?hitchhikers_guide_to_rfid>
+
+=head1 Data model
+
+=head2 3M Alphanumeric tag
+
+ 0 04 is 00 tt i [4 bit] = number of item in set [1 .. i .. s]
+ s [4 bit] = total items in set
+ tt [8 bit] = item type
+
+ 1 dd dd dd dd dd [16 bytes] = barcode data
+ 2 dd dd dd dd
+ 3 dd dd dd dd
+ 4 dd dd dd dd
+
+ 5 bb bl ll ll b [12 bit] = branch [unsigned]
+ l [20 bit] = library [unsigned]
+
+ 6 cc cc cc cc c [32 bit] = custom signed integer
+
+=head2 3M Manufacturing Blank
+
+ 0 55 55 55 55
+ 1 55 55 55 55
+ 2 55 55 55 55
+ 3 55 55 55 55
+ 4 55 55 55 55
+ 5 55 55 55 55
+ 6 00 00 00 00
+
+=head2 Generic blank
+
+ 0 00 00 00 00
+ 1 00 00 00 00
+ 2 00 00 00 00