How come the format and parse tokens Yand D are protected, but not all their lengths and variants?

I'm guessing it was put in place to help people migrate from other libraries, but the Y, YYYYY, YYYYYY are valid in moment too. DDD and DDDD behave the same in both, so it's probably not impactful for migration mistakes.

EDIT: not quite the same in terms of padding, though. Ex: Jan 3rd 2021:

I wouldn't rule out that this protection feature is also helping people that are simply just guessing the tokens without consulting the docs. If the output looks OK at first glance, it probably ships and creates weird bugs in many apps, especially Y.

See #2133

Just wanted to put this out there, and suggest that all variants should be protected in v3.

import { format } from "date-fns";

const now = new Date(2021, 11, 29);

const tokens = [
  "Yo",
  "Y",
  "YY",
  "YYY",
  "YYYY",
  "YYYYY",
  "YYYYYY",
  "Do",
  "D",
  "DD",
  "DDD",
  "DDDD",
  "DDDDD",
  "DDDDDD"
];

tokens.forEach((t) => {
  try {
    console.log(t, format(now, t));
  } catch (e) {
    console.log(t, "Range Error");
  }
});

// Yo 2022nd 
// Y 2022 
// YY Range Error 
// YYY 2022 
// YYYY Range Error 
// YYYYY 02022 
// YYYYYY 002022 

// Do 363rd 
// D Range Error 
// DD Range Error 
// DDD 363 
// DDDD 0363 
// DDDDD 00363 
// DDDDDD 000363 

Related:
https://date-fns.org/docs/format
https://date-fns.org/docs/parse
https://github.com/date-fns/date-fns/blob/master/docs/unicodeTokens.md