IIRC it was basically undefined, some data formats were defined. Eventually it was specified that it must correctly parse RFC 3339 and everything was browser defined. I think in the name of web compatibility they have started to carefully define the legacy behaviours of common browsers.
But the morale of this story should be if you need a date from a user user a date input and if you need to parse a computer-readable date always use UNIX timestamps or RFC 3339 (which are correctly and consistently supported).
IIRC it was basically undefined, some data formats were defined. Eventually it was specified that it must correctly parse RFC 3339 and everything was browser defined. I think in the name of web compatibility they have started to carefully define the legacy behaviours of common browsers.
But the morale of this story should be if you need a date from a user user a date input and if you need to parse a computer-readable date always use UNIX timestamps or RFC 3339 (which are correctly and consistently supported).