diff --git a/src/suou/__init__.py b/src/suou/__init__.py
index 4a14073..9d12a76 100644
--- a/src/suou/__init__.py
+++ b/src/suou/__init__.py
@@ -27,7 +27,7 @@ from .itertools import makelist, kwargs_prefix, ltuple, rtuple, additem
 from .i18n import I18n, JsonI18n, TomlI18n
 from .snowflake import Snowflake, SnowflakeGen
 
-__version__ = "0.4.0-dev26"
+__version__ = "0.4.0-dev27"
 
 __all__ = (
     'Siq', 'SiqCache', 'SiqType', 'SiqGen', 'StringCase',
diff --git a/src/suou/classtools.py b/src/suou/classtools.py
index 34ad58b..6362b81 100644
--- a/src/suou/classtools.py
+++ b/src/suou/classtools.py
@@ -18,13 +18,19 @@ from __future__ import annotations
 
 from abc import ABCMeta, abstractmethod
 from typing import Any, Callable, Generic, Iterable, Mapping, TypeVar
+import logging
 
 from suou.codecs import StringCase
 
 _T = TypeVar('_T')
 
+logger = logging.getLogger(__name__)
+
 MISSING = object()
 
+def _not_missing(v) -> bool:
+    return v and v is not MISSING
+
 class Wanted(Generic[_T]):
     """
     Placeholder for parameters wanted by Incomplete().
@@ -106,6 +112,8 @@ class Incomplete(Generic[_T]):
         return clsdict
 
 
+## Base classes for declarative argument / option parsers below
+
 class ValueSource(Mapping):
     """
     Abstract value source.
@@ -158,6 +166,10 @@ class ValueProperty(Generic[_T]):
             for srckey, src in self._srcs.items():
                 if (getter := self._getter(obj, srckey)):
                     v = getter.get(src, v)
+                    if _not_missing(v):
+                        if srckey != 'default':
+                            logger.info(f'value {self._name} found in {srckey} source')
+                        break
             if self._required and (not v or v is MISSING):
                 raise self._not_found(f'required config {self._srcs['default']} not set!')
             if v is MISSING: