Is "0" a valid XML duration?

[Rod Widdowson]

I turned on noisy logging for Spring to help me understand how the bean
loading works.  

Amongst all the "aggravating but benign" exceptions it throws I saw one from
DurationToLongConverter: "Durations must start with 'P'".

And this was because we have  idp.session.slop = 0 in idp.properties.  

In fact this is just another "benign but aggravating" exception because the
built-in spring converters then do the right thing.  

I am just idly wondering 

1) whether "0" is a valid duration and regardless of whether it is or not
2) whether it is worthwhile to teach DurationToLongConverter to understand
"0".

/Rod