def __contains__(self, feature: Preview) -> bool:
        """
        Provide `Preview.FEATURE in Mode` syntax that mirrors the ``preview`` flag.

        In unstable mode, all features are enabled. In preview mode, all features
        except those in UNSTABLE_FEATURES are enabled. Any features in
        `self.enabled_features` are also enabled.
        """
        if self.unstable:
            return True
        if feature in self.enabled_features:
            return True
        return self.preview and feature not in UNSTABLE_FEATURES

        Provide `Preview.FEATURE in Mode` syntax that mirrors the ``preview`` flag.

        In unstable mode, all features are enabled. In preview mode, all features
        except those in UNSTABLE_FEATURES are enabled. Any features in
        `self.enabled_features` are also enabled.
        
src/black/mode.py