The Vital Sign Observation template says:

Use a default of 1 for @unit when @nullFlavor is present.

But we've awkwardly got this in the Vital Sign Average Blood Pressure Example:

<value xsi:type="PQ" nullFlavor="NA" unit="{NA}" />

I'm definitely not a fan of the unit="{NA}" shenanigans going on here. Ideally, I think, we want to just be able to have:

<value xsi:type="PQ" nullFlavor="NA" />

and only require the @unit to be present if a @nullFlavor isn't. In such cases, I think the unit for a PQ is implicitly 1 anyway, so it's possible that we can just do this already and we just need to change the example.

If the validator really will throw a fuss if we don't have a @unit attribute, though, and we think it's correct for it to do that in this case, can we at least change the example to value xsi:type="PQ" nullFlavor="NA" unit="1" />?

I guess this might just be my personal sense of aesthetics, but @unit="{NA}" feels like an ugly workaround to me and suggests that we might have a problem with the way the template handles the @unit requirement. I'd rather change that before encouraging @unit="{NA}" as a best practice.