<xsd:documentation>A measure value.
Unless the parameter is defined as a tuple, only one value should be specified.
The measure class is defined by measureClass in the parent set.
The unit of measure must conform to the units allowed by the measure class
in the unit dictionary file.
If the 'status' attribute is absent and the value is not "NaN",
the data value can be assumed to be good with no restrictions.
A value of "NaN" should be interpreted as null and should be not be given unless
a status is also specified to explain why it is null.</xsd:documentation>