Note that type variables can be *bound*, *constrained*, or neither, but
cannot be both bound *and* constrained.
- Created type variables may be explicitly marked covariant or contravariant by passing
- ``covariant=True`` or ``contravariant=True``.
- By default, type variables are invariant.
- See :pep:`484` and :pep:`695` for more details.
+ Type variables may be marked covariant or contravariant by passing
+ ``covariant=True`` or ``contravariant=True``. See :pep:`484` for more
+ details. By default, type variables are invariant.
Bound type variables and constrained type variables have different
semantics in several important ways. Using a *bound* type variable means