class Foo(HasProps): x = bcpd.DistanceSpec(default=14)
class FooUnits(HasProps): x = bcpd.DistanceSpec("x")
class Foo(HasProps): x = bcpd.DistanceSpec(None)
class Foo(HasProps): x = bcpd.DistanceSpec(default=14)
class FooUnits(HasProps): x = bcpd.DistanceSpec("x")
class Foo(HasProps): x = bcpd.DistanceSpec(None)