---
features:
  - |
    Contexts may now have transaction constraints set on them to be enforced
    by the revision plugin in Neutron for generalized compare-and-swap updates.
    Calling ``set_transaction_constraint`` on the context before performing a
    resource mutation will setup the constraint. This is also exposed to users
    via the HTTP API with ``if-match`` headers and the API layer sets the
    constraint on the context.
