The UV Use Period template specifies that the effectiveTime/low element should have cardinality NP when a width is present.

I'm not sure what the correct way is to interpret NP in ART-DECOR, but it seems like there's one of two problems here:

1) If NP means "we're not putting any constraints on this element, feel free to include it or not" then why mention it at all?

2) Alternatively, if NP means "this element shall not be included" (and I'm guessing this is the likelier of the two interpretations" then why? In particular, it seems like this is a totally reasonable way to specify that a med's duration should begin on Sep 1 and last two weeks:

<effectiveTime xsi:type="IVL_TS">
  <low value="20220901" />
  <width value="14" unit="d" />
</effectiveTime>

If there's a really strong desire not to do that (perhaps you should just specify an effectiveTime/high instead in that case?) and the intention is that if you have a width, you should have neither a low nor a high, then should it also specify NP as the cardinality for the high element?

No matter which way this goes, it seems like something needs to be added here to make it clearer.