For backward compatibility, loading or dumping unsafe YAML contents only produce a DeprecationWarning if the function has not been explicitly called with a `safe` argument.
Loading or dumping with `safe=False` causes behavior identical to releases predating this one.
Loading or dumping with `safe=True` will ensure that only safe contents are allowed. Contents deemed unsafe by the pyyaml module will raise a SerializationSafetyError.