.validate() on serializer fields

rest_framework/fields.py

@@ -254,6 +254,7 @@ class Field(object):
 
         value = self.to_internal_value(data)
         self.run_validators(value)
+        self.validate(value)
         return value
 
     def run_validators(self, value):
@@ -270,6 +271,9 @@ class Field(object):
         if errors:
             raise ValidationError(errors)
 
+    def validate(self, value):
+        pass
+
     def to_internal_value(self, data):
         """
         Transform the *incoming* primative data into a native value.