the type of the property descriptor may be changed and the property may be deleted from the corresponding object.
the property shows up during enumeration of the properties on the corresponding object.
the value associated with the property may be changed with an assignment operator. This doesn't have any effect when passed to jsc_value_object_define_property_accessor().
Flags used when defining properties with jsc_value_object_define_property_data() and jsc_value_object_define_property_accessor().