diff --git a/dcd/aux.py b/dcd/aux.py
index 39af873..c33f900 100644
--- a/dcd/aux.py
+++ b/dcd/aux.py
@@ -77,3 +77,32 @@ def hex_to_raw(text, separator=" "):
 	return bytearray(output)
 
 # ----------------------------------------------------------------
+
+class DeleteOverlay:
+	pass
+
+def overlay_tree(base, overlay):
+	"""
+	For every key path in `overlay`, sets the leaf value of the same
+	key path in `base`. Any missing non-leaf keys will be created.
+	
+	To delete a key, set its overlay value to DeleteOverlay.
+	"""
+	
+	stack = [(base, overlay)]
+	
+	while stack:
+		base_p, over_p = stack.pop()
+		
+		for k, v in over_p.items():
+			if v is DeleteOverlay:
+				del base_p[k]
+			else:
+				if type(v) is dict:
+					if k not in base_p or type(base_p[k]) is not dict:
+						base_p[k] = {}
+					
+					stack.append((base_p[k], over_p[k]))
+				
+				else:
+					base_p[k] = v
diff --git a/dcd/cfg.py b/dcd/cfg.py
index 4f0053a..b062463 100644
--- a/dcd/cfg.py
+++ b/dcd/cfg.py
@@ -4,6 +4,18 @@
 import jsmin
 import json
 
+from . import aux
+
+def _read_json(path):
+	"""
+	Reads a data structure from a JSON file pointed to by `path`.
+	
+	Removes any C/JS-like comments from it.
+	"""
+	
+	with open(path) as f:
+		return json.loads(jsmin.jsmin(f.read()))
+
 class Config:
 	"""
 	A hierarchical key-value container that can be loaded from JSON or a Python dict.
@@ -11,48 +23,30 @@ class Config:
 	Any contained dicts are automatically converted to Config instances as well.
 	
 	Supports sequential overwriting - so one can load a default config and then
-	progressively overwrite it with overlays:
-	
-	
-	
-	
-	
-	
-	
-	>>> raw
-{'a': 1, 'b': {'ba': 2, 'bb': 3, 'bc': {'bca': None}}, 'c': 4}
->>> overlay
-{'b': {'bc': {'bca': 42}}}
-
-	
-	
-	while stack:
-	current = stack[-1]
-	
-	...
-	
-	stack.pop()
-
-for key in overlay.keys():
-	
-	
+	progressively overlay more on top:
 	
+	>>> c = Config.from_file("/usr/lib/app/default.cfg")
+	>>> c.update_from_file("/etc/app/config.cfg")
+	>>> c.update({"key", value, "subtree": {"key": "value"}})
 	"""
 	
-	def __init__(self, d, readonly=False):
+	def __init__(self, d=None, readonly=False):
+		if d is None:
+			d = {}
+		
 		assert type(d) == dict
 		object.__setattr__(self, "raw", d)
 		object.__setattr__(self, "readonly", readonly)
 	
 	@classmethod
 	def from_file(cls, path, readonly=False):
-		with open(path) as f:
-			initial = json.loads(jsmin.jsmin(f.read()))
-		
-		return cls(initial, readonly)
+		return cls(_read_json(path), readonly)
 	
 	def update(self, d):
-		
+		aux.overlay_tree(self.raw, d)
+	
+	def update_from_file(self, path):
+		self.update(_read_json(path))
 	
 	def keys(self):
 		return self.raw.keys()
diff --git a/setup.py b/setup.py
old mode 100644
new mode 100755