--- a/configmix/config.py	Sun Dec 19 16:33:31 2021 +0100
+++ b/configmix/config.py	Sun Dec 19 18:37:37 2021 +0100
@@ -696,6 +696,8 @@
         `key` must be a configuration reference URI without any
         (namespace) prefixes and suffixes
 
+        :raise KeyError: If the reference is not found
+
         """
         return self.expand_ref_uri(key)
 
@@ -720,6 +722,11 @@
             return v
 
     def expand_ref_uri(self, uri):
+        """
+
+        :raises KeyError: If the reference URI is not found
+
+        """
         pu = urlsplit(uri)
         if pu.scheme or pu.netloc or pu.path or pu.query:
             raise ValueError("only fragment-only URIs are supported")