20621 2013-01-09 19:02:29 +0000 valid time string point 4 is oddly expressed 2013-03-07 23:04:37 +0000 1 1 1 Unclassified WHATWG HTML unspecified All All RESOLVED WORKSFORME P2 normal Unsorted 1 mounir ian ian mike contributor oldest_to_newest 81141 0 mounir 2013-01-09 19:02:29 +0000 http://www.whatwg.org/specs/web-apps/current-work/multipage/common-microsyntaxes.html#valid-time-string Point 4 is here to say that: HH:mm is a valid time string because it is implicitely equivalent to HH:mm:00. I would suggest to remove the "(required if second is non-zero)" part. A time string is valid if it is on the following formats: HH:mm or HH:mm:ss or HH:mm:ss.sss. "Valid time string" isn't there to convert the string to a computer-readable time. Only to check if a given string represents a time. Converting a string to a computer-readable time is the role of "Parse a time string": http://www.whatwg.org/specs/web-apps/current-work/multipage/common-microsyntaxes.html#parse-a-time-string This also applies to 4.3. 84090 1 ian 2013-03-07 23:04:37 +0000 That part of the spec is giving the conformance requirements for writing a valid time string representing a specific time. If the specific time being represented is one second past noon, then the string "12:00" would _not_ be a valid time string for it.