  This document describes a recommended syntax for writing the string
representation of unit labels ("VOUnits"). In addition, it describes a set of
recognised and deprecated units, which is as far as possible consistent with
other relevant standards (BIPM, ISO/IEC and the IAU). The intention is that
units written to conform to this specification will likely also be parsable by
other well-known parsers. To this end, we include machine-readable grammars for
other units syntaxes.
