diff --git a/rdflib/namespace.py b/rdflib/namespace.py
index b3eddaa62..084646c2d 100644
--- a/rdflib/namespace.py
+++ b/rdflib/namespace.py
@@ -144,6 +144,20 @@ def __repr__(self):
         return f"Namespace({self!r})"
 
     def __contains__(self, ref):
+        """Allows to check if a URI is within (starts with) this Namespace.
+
+        >>> from rdflib import URIRef
+        >>> namespace = Namespace('http://example.org/')
+        >>> uri = URIRef('http://example.org/foo')
+        >>> uri in namespace
+        True
+        >>> person_class = namespace['Person']
+        >>> person_class in namespace
+        True
+        >>> obj = URIRef('http://not.example.org/bar')
+        >>> obj in namespace
+        False
+        """
         return ref.startswith(self) # test namespace membership with "ref in ns" syntax
 
 
diff --git a/test/test_namespace.py b/test/test_namespace.py
index a36376f94..59ff0ecec 100644
--- a/test/test_namespace.py
+++ b/test/test_namespace.py
@@ -1,10 +1,21 @@
 import unittest
 
 from rdflib.graph import Graph
-from rdflib.namespace import Namespace, FOAF, RDF, RDFS, SH
+from rdflib.namespace import Namespace, FOAF, RDF, RDFS, SH, DCTERMS
 from rdflib.term import URIRef
 
 
+class NamespaceTest(unittest.TestCase):
+    def test_dcterms_title(self):
+        self.assertEqual(DCTERMS.title, URIRef(DCTERMS + 'title'))
+
+    def test_iri(self):
+        prefix = u'http://jörn.loves.encoding.problems/'
+        ns = Namespace(prefix)
+        self.assertEqual(ns, str(prefix))
+        self.assert_(ns[u'jörn'].startswith(ns))
+
+
 class NamespacePrefixTest(unittest.TestCase):
     def test_compute_qname(self):
         """Test sequential assignment of unknown prefixes"""