I am reading and taking notes on the HTML specifications for 100 days as part of #The100DayProject. Read the initial intent/backstory. I am a Microsoft employee but all opinions, comments, etc on this site are my own. I do not speak on behalf of my employer, and thus no comments should be taken as representative of Microsoft's official opinion of the spec. Subsections not listed below were read without comment.
Currently reading in 2.4 Common microsyntaxes, dates and times.
A duration is a number of seconds. I wrote "quite simply" at first and then backspaced over that right quick because look.
One does not simply convert months/years into seconds. BUT you can give a duration in units of weeks, days, hours, minutes, and seconds.
The algorithm for parsing the duration string has quite a few steps, including but not limited to FUN WITH LOOPS!
18.104.22.168 Vaguer moments in time
Heh, I like the title of this subsection. This describes a "valid date string with optional time" and how to parse it. I think in order to understand what that actually means, I'd probably have to go back over the algorithms and compare differences. Seeing as I don't need to know that level of depth to do my work, I'm going to say "meh" and move right along from the "Dates and times" subsection of "Common Microsyntaxes".