40,000,000 seconds is 462.962 days. If I wanted to represent that as an ISO-8601 period, in this form:
PnYnMnDTnHnMnS
What are the rules for determining months and years? Neither are precise terms, and the standard says that it depends on the start date of the period.
This makes sense: it makes the period ambiguous without a start date. Are there any accepted means of using a period without a start date?