Hi Tim, The only one concern I see is the method `fromIso8601String`. Unfortunately the PHP has this weird constant that is called DATE_ISO8601 https://www.php.net/manual/en/class.datetimeinterface.php#datetimeinterface.constants.iso8601, that is not in fact proper standard.
I wanted to deprecate it few years ago, but the push back from community was strong, so I did suggest only deprecation of DATE_RFC7231. So what kind of format this method will except, standard ISO, or PHP's version of ISO? Maybe it's worth to find another name? Kind regards, Jorg
