Checks for appropriate units using Pint unit registry.
        Args:
            isvalid_unit (`bool`): flag from schema indicating units to be checked.
            field (`str`): property associated with units in question.
            value (`dict`): dictionary of values from file associated with this property.

        The rule's arguments are validated against this schema:
            {'isvalid_unit': {'type': 'bool'}, 'field': {'type': 'str'},
             'value': {'type': 'dict'}}

def _validate_isvalid_unit(self, isvalid_unit, field, value):
        """Checks for appropriate units using Pint unit registry.
        Args:
            isvalid_unit (`bool`): flag from schema indicating units to be checked.
            field (`str`): property associated with units in question.
            value (`dict`): dictionary of values from file associated with this property.

        The rule's arguments are validated against this schema:
            {'isvalid_unit': {'type': 'bool'}, 'field': {'type': 'str'},
             'value': {'type': 'dict'}}
        """
        quantity = 1.0 * units(value['units'])
        try:
            quantity.to(property_units[field])
        except pint.DimensionalityError:
            self._error(field, 'incompatible units; should be consistent '
                        'with ' + property_units[field]
                        )