title: What is the value of the ISO 8601 duration `P1M` (in seconds)?
body: <p>Suppose I have an ISO 8601 duration, expressed as <code>"P1M"</code>. Phrased colloquially, this means "one month." Is there a standard rule for converting this into a number of seconds, assuming the start date is not known?</p>
  
  <ul>
  <li>For 30-day months, it might be 2,592,000.</li>
  <li>For 31-day months, it might be 2,678,400.</li>
  <li>In February, it might be 2,419,200 or it might be 2,505,600.</li>
  </ul>
  
  <p>My gut says there's no way to resolve "one month" to an exact number of seconds without knowing context, and where those seconds are laid out on the calendar. But are there standard rules/conventions to calculate these durations in an abstract way?</p>