The Outline Processor Markup Language (OPML) is an XML format for outlines, that is mostly used to exchange lists of web feeds between web feed aggregrators. It uses the RFC 822 date format, which is considered obsolete. Fans of the RFC 822 date think it’s a good idea to have only two digits to represent a year. But I have no idea if they were born 1900 or 2000 or if they’ve ever heard of the much cooler RFC 3339. Or how they would call it: RF 39. Anyway. You’re here because you want to use this format. Or you have to. My condolences.