Which function returns a correct ISO8601 date?

Hi, all Some days ago, I needed a date, formatted as date("c") ... To be a bit more object-oriented, I worked with an instance of DateTime. My first thought was: "As the documenting for date() defines 'c' as ISO8601, I can take the constant provided in the DateTime object ... right?" ... and that was wrong. Here's a code-example: date("c"); // 2013-09-07T12:40:25+00:00 date(DateTime::ISO8601); // 2013-09-07T12:40:25+0000 -> Take special care to the notation of the timezone. The method date("c") actually formats a date, fitting to the format defined in the constant DateTime::ATOM. Are both formats (with and without colon) valid for ISO8601, or is the documentation for the method date() wrong? Bye, Simon