EML

The precision field in eml-attribute is defined circularly and needs to be
changed. In addition, although it is a fundamental part of attribute metadata,
sometimes it is not available and because it is required it would prevent people
from providing the rest of the attribute metadata that they may have.

Proposal: Change definition as below, and change cardinality to optional.

Proposed definition:
Precision indicates how close together or how repeatable measurements are. A
precise measuring instrument will give very nearly the same result each time it
is used. This means that someone interpreting the data should expect that if a
measurement were repeated, most measured values would fall within the interval
specified by the precision. The value of precision should be expressed in the
same unit as the measurement. For example, for an attribute with unit "meter", a
precision of "0.1" would be interpreted to mean that most repeat measurements
would fall within an interval of 1/10th of a meter.