diff --git a/ipalib/plugable.py b/ipalib/plugable.py
index c3eb409b0..4032b574e 100644
--- a/ipalib/plugable.py
+++ b/ipalib/plugable.py
@@ -54,6 +54,23 @@ def check_identifier(name):
     	raise errors.NameSpaceError(name, regex)
 
 
+class Abstract(object):
+    __public__ = frozenset()
+
+    @classmethod
+    def implements(cls, arg):
+        assert type(cls.__public__) is frozenset
+        if isinstance(arg, str):
+            return arg in cls.__public__
+        if type(getattr(arg, '__public__', None)) is frozenset:
+            return cls.__public__.issuperset(arg.__public__)
+        if type(arg) is frozenset:
+            return cls.__public__.issuperset(arg)
+        raise TypeError(
+            "must be str, frozenset, or have frozenset '__public__' attribute"
+        )
+
+
 class Plugin(object):
     """
     Base class for all plugins.
diff --git a/ipalib/public.py b/ipalib/public.py
index 6f7f21540..1c6f9e7f8 100644
--- a/ipalib/public.py
+++ b/ipalib/public.py
@@ -102,7 +102,7 @@ class option(object):
     def __rules_iter(self):
     	"""
     	Iterates through the attributes in this instance to retrieve the
-    	methods implemented validation rules.
+    	methods implementing validation rules.
     	"""
     	for name in dir(self.__class__):
     		if name.startswith('_'):
@@ -117,6 +117,10 @@ class option(object):
     	"""
     	Returns a default or auto-completed value for this option. If no
     	default is available, this method should return None.
+
+    	All the keywords are passed so it's possible to build an
+    	auto-completed value from other options values, e.g., build 'initials'
+    	from 'givenname' + 'sn'.
     	"""
     	return None
 
@@ -177,11 +181,15 @@ class cmd(plugable.Plugin):
     			self.options.validate(value)
 
     def default(self, **kw):
+        d = {}
     	for opt in self.options:
     		if opt.name not in kw:
     			value = opt.default(**kw)
     			if value is not None:
-    				kw[opt.name] = value
+    				d[opt.name] = value
+    	assert not set(kw).intersection(d)
+    	kw.update(d)
+    	return kw
 
     def __call__(self, **kw):
     	(args, kw) = self.normalize(*args, **kw)
diff --git a/ipalib/tests/test_public.py b/ipalib/tests/test_public.py
index f396eed28..49fbb17f2 100644
--- a/ipalib/tests/test_public.py
+++ b/ipalib/tests/test_public.py
@@ -63,13 +63,35 @@ def test_is_rule():
     assert not is_rule(call(None))
 
 
-class test_option():
-    def cls(self):
-    	return public.option
+class ClassChecker(object):
+    __cls = None
+    __subcls = None
 
-    def sub(self):
+    def __get_cls(self):
+        if self.__cls is None:
+            self.__cls = self._cls
+        return self.__cls
+    cls = property(__get_cls)
+
+    def __get_subcls(self):
+        if self.__subcls is None:
+            self.__subcls = self.get_subcls()
+        return self.__subcls
+    subcls = property(__get_subcls)
+
+    def get_subcls(self):
+        raise NotImplementedError(
+            self.__class__.__name__,
+            'get_subcls()'
+        )
+
+
+class test_option(ClassChecker):
+    _cls = public.option
+
+    def get_subcls(self):
     	rule = public.rule
-    	class int_opt(self.cls()):
+    	class int_opt(self.cls):
     		type = int
     		@rule
     		def rule_0(self, value):
@@ -89,13 +111,12 @@ class test_option():
     	"""
     	Perform some tests on the class (not an instance).
     	"""
-    	cls = self.cls()
     	#assert issubclass(cls, plugable.ReadOnly)
-    	assert type(cls.rules) is property
+    	assert type(self.cls.rules) is property
 
     def test_normalize(self):
-    	sub = self.sub()
-    	i = sub()
+        assert 'normalize' in self.cls.__public__
+    	o = self.subcls()
     	# Test with values that can't be converted:
     	nope = (
     		'7.0'
@@ -104,7 +125,7 @@ class test_option():
     		None,
     	)
     	for val in nope:
-    		e = raises(errors.NormalizationError, i.normalize, val)
+    		e = raises(errors.NormalizationError, o.normalize, val)
     		assert isinstance(e, errors.ValidationError)
     		assert e.name == 'int_opt'
     		assert e.value == val
@@ -120,29 +141,36 @@ class test_option():
     		' 7 ',
     	)
     	for val in okay:
-    		assert i.normalize(val) == 7
+    		assert o.normalize(val) == 7
+
+    def test_validate(self):
+    	"""
+    	Test the validate method.
+    	"""
+    	assert 'validate' in self.cls.__public__
+    	o = self.subcls()
+    	o.validate(9)
+    	for i in xrange(3):
+    		e = raises(errors.RuleError, o.validate, i)
+    		assert e.error == 'cannot be %d' % i
+    		assert e.value == i
 
     def test_rules(self):
     	"""
     	Test the rules property.
     	"""
-    	o = self.sub()()
+    	o = self.subcls()
     	assert len(o.rules) == 3
     	def get_rule(i):
     		return getattr(o, 'rule_%d' % i)
     	rules = tuple(get_rule(i) for i in xrange(3))
     	assert o.rules == rules
 
-    def test_validation(self):
-    	"""
-    	Test the validation method.
-    	"""
-    	o = self.sub()()
-    	o.validate(9)
-    	for i in xrange(3):
-    		e = raises(errors.RuleError, o.validate, i)
-    		assert e.error == 'cannot be %d' % i
-    		assert e.value == i
+    def test_default(self):
+        assert 'default' in self.cls.__public__
+        assert self.cls().default() is None
+
+