          self.lookup_field = kwargs.pop('lookup_field', self.lookup_field)
          self.lookup_url_kwarg = kwargs.pop('lookup_url_kwarg', self.lookup_field)
          self.format = kwargs.pop('format', None)
  
          # We include these simply for dependancy injection in tests.
          # We can't add them as class attributes or they would expect an
          # implict `self` argument to be passed.
          self.reverse = reverse
          self.resolve = resolve
  
 
</s> remove     # Allow dependancy injection of other settings to make testing easier.
 </s> add     # Allow dependency injection of other settings to make testing easier. </s> remove * `WriteableField` as the base class for read-write fields.
 </s> add * `WritableField` as the base class for read-write fields. </s> remove         # consider it, or treat PIL as a test dependancy.
 </s> add         # consider it, or treat PIL as a test dependency. </s> remove * Some data, such as many-to-many relationships, cannot be added to the object instance until after it has been saved. This type of data needed to be hidden in some undocumentated state on the object instance, or kept as state on the serializer instance so that it could be used when `.save()` is called.
 </s> add * Some data, such as many-to-many relationships, cannot be added to the object instance until after it has been saved. This type of data needed to be hidden in some undocumented state on the object instance, or kept as state on the serializer instance so that it could be used when `.save()` is called. </s> remove We now have a better seperation, with seperate `required` and `allow_none` arguments.
 </s> add We now have a better separation, with separate `required` and `allow_none` arguments.
        # We include these simply for dependency injection in tests.
          self.lookup_field = kwargs.pop('lookup_field', self.lookup_field)
          self.lookup_url_kwarg = kwargs.pop('lookup_url_kwarg', self.lookup_field)
          self.format = kwargs.pop('format', None)
  
        # We include these simply for dependency injection in tests.
          # We can't add them as class attributes or they would expect an
          # implict `self` argument to be passed.
          self.reverse = reverse
          self.resolve = resolve
  
keep keep keep keep replace keep keep keep keep keep
 Minor: fix spelling and grammar, mostly in 3.0 announcement 
rest_framework/relations.py