I'll take this opportunity and also point out a pet peeve of mine with this spec in section 7:<p>The Luhn algorithm used as a check digit is suboptimal; better options with greater detection rates of various kinds of human input errors exist, see e.g. <a href="https://www.uni-due.de/imperia/md/content/dc/yanling_2015_check_digit.pdf" rel="nofollow">https://www.uni-due.de/imperia/md/content/dc/yanling_2015_ch...</a>, p. 12 also showing some other options. See also <a href="http://page.mi.fu-berlin.de/rhschulz/Literatur/checkdigits_literatur.pdf" rel="nofollow">http://page.mi.fu-berlin.de/rhschulz/Literatur/checkdigits_l...</a> for further reading on check digits.