DMNFTF — support for 'duration'

Clause 10.3.1.3 says:
"FEEL supports the following datatypes:
...

• duration
  o days and time duration
  o years and months duration"
  But 10.3.2 only defines the two subtypes, which correspond to XPath Datamodel datatypes, which are respectively integer counts of seconds and months. It does not refer to the XML Schema 'duration' type.

Similarly, the "duration" function in clause 10.3.4.1 requires the string value to be in the lexical space of one of these two subtypes, not that of xs:duration, per footnote 6 to table 54 (beta-3) [Note: the footnote erroneously refers to Xpath. It should be XDM.]

It is apparently not intended that a supporting tool needs to support xs:duration at all. For that reason, the supertype 'duration' should be omitted from the list in 10.3.1.3. Alternatively, it might say that support for the more general 'duration' type is not required.

Finally, 10.3.4.1 defines a function that produces a yearMonthDuration as the difference between two date/time values (which presumably truncates the duration result), but no function that produces a dayTimeDuration (which could be exact). This is a shortcoming for stating rules relating to elapsed time.

Remove 'duration' from the list in 10.3.1.3 and elevate the two sub-bullets:

• years and months duration
• days and time duration