So it's not even a subset of ISO 8601, it's just the umpteenth ad-hoc date parsing method with semantics defined as "portion of a 3k line C file with no comment

So it's not even a subset of ISO 8601, it's just the umpteenth ad-hoc date parsing method with semantics defined as "portion of a 3k line C file with no comments": https://github.com/ruby/ruby/blob/7ea675732ac1dac72f07756498706678d8725719/ext/date/date_parse.c#L2600 https://github.com/ruby/ruby/blob/7ea675732ac1dac72f07756498... PS I did my undergrad thesis on Ruby; I love the language. But now that I have a job where people read my code more often than it's written, I understand why things like clear semantics matter. And why method names should be precise since they lead developers to assume behavior. Didn't your english teacher tell you a poem's title means something? So do method names. "iso8601" implies some meaningful relationship to ISO 8601, but the only relationship here is that the coders of this method were thinking hard about ISO 8601 when they wrote it.