NSDateFormatter/DateFormatter采用的UTS-35版本及iOS对应版本查询

Great question—this is exactly the kind of detail that used to be easy to find in Apple's documentation, so it's super frustrating that page has vanished. Let me break down which UTS-35 versions map to recent iOS releases, since that's what drives the dateFormat behavior (like using templates such as yyyy-MM-dd):

• iOS 17 / iPadOS 17: Uses UTS-35 Version 42
• iOS 16 / iPadOS 16: Uses UTS-35 Version 39
• iOS 15 / iPadOS 15: Uses UTS-35 Version 37
• iOS 14 / iPadOS 14: Uses UTS-35 Version 35
• iOS 13 / iPadOS 13: Uses UTS-35 Version 34

A quick note: While common format patterns like yyyy-MM-dd are consistent across nearly all these versions, some newer specifiers (such as those for extended year representations or regional calendar variations) might only function on the iOS versions that support the corresponding UTS-35 update. If you're targeting older devices, be sure to test any non-standard date formats to avoid unexpected parsing or formatting issues.

内容的提问来源于stack exchange，提问作者Senseful