Unfortunately not, for the project I'm working on right now I only needed 'forward' durations. There's a W3C extension that proposes a preceding - sign for nega

Unfortunately not, for the project I'm working on right now I only needed 'forward' durations. There's a W3C extension that proposes a preceding - sign for negative durations, which I think it's fair https://www.w3.org/TR/xmlschema-2/#duration https://www.w3.org/TR/xmlschema-2/#duration. The ISO standard explicitly declares durations to be non-negative, on the other hand. As close to canonical as you can get.