A count of a discrete element (no unit)
There SHALL be a code with a value of "1" if there is a value and it SHALL be an expression of length. If system is present, it SHALL be UCUM. If present, the value SHALL a whole number.
XPath:
(f:code or not(f:value)) and (not(exists(f:system)) or (f:system/@value='http://unitsofmeasure.org' and f:code/@value='1')) and not(contains(f:value/@value, '.'))