Notes on payment cards and card data: BIN/IIN lookups, the move to 8-digit issuer numbers, 3-D Secure, and how the card networks structure a PAN.
The card networks expanded the issuer identifier on a payment card from 6 to 8 digits. For anyone doing BIN/IIN lookups it means a 6-digit prefix is no longer guaranteed to identify a single issuer — you often need 8 digits to disambiguate. Here's the what, the why, and the practical fallout.
In 2013, sitting on a balcony in Playitas, Fuerteventura, I built binlist.net as my first ever Go project — a free HTTP API for looking up the issuer of a credit card from its first six digits. It hit 1 million queries/day by 2015. Thirteen years later it's still free, and its commercial sibling iinlist.com is the one we run the business on.
xmllint (part of libxml2, already on most systems) reformats ugly, minified, or single-line XML into something readable. Pipe an API response straight through it, control the indent width, and validate while you're at it.