@abc.abstractproperty<EOL><INDENT>def properties(self):<DEDENT>
Properties of entry as a :class:`Mapping` subclass (e.g. dict).

        Note that the properties are not generally mutable but may be mutable
        for specific subclasses. If the ``id`` exists in this dictionary, it
        must never change the actual entry ID as obtained from the ``id``
        property, even if other properties are mutable.