They're very different from the format strings in Python, which takes format strings from the [C standard library](https://en.cppreference.com/w/c/chrono/strfti

They're very different from the format strings in Python, which takes format strings from the [C standard library](https://en.cppreference.com/w/c/chrono/strftime https://en.cppreference.com/w/c/chrono/strftime), which is different from (and older than) these Unicode format srrings. Same holds for other libc based languages like Perl or R. JS does not have native datetime format strings AFAIK, and 3rd party libs such as moment.js often invent their own strings.