--- a/genshi/builder.py
+++ b/genshi/builder.py
@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 #
-# Copyright (C) 2006-2007 Edgewall Software
+# Copyright (C) 2006-2008 Edgewall Software
 # All rights reserved.
 #
 # This software is licensed as described in the file COPYING, which
@@ -68,7 +68,13 @@
 Hello, <em>world</em>!
 """
 
-from genshi.core import Attrs, Namespace, QName, Stream, START, END, TEXT
+try:
+    set
+except NameError:
+    from sets import Set as set
+
+from genshi.core import Attrs, Markup, Namespace, QName, Stream, \
+                        START, END, TEXT
 
 __all__ = ['Fragment', 'Element', 'ElementFactory', 'tag']
 __docformat__ = 'restructuredtext en'
@@ -107,6 +113,9 @@
     def __unicode__(self):
         return unicode(self.generate())
 
+    def __html__(self):
+        return Markup(self.generate())
+
     def append(self, node):
         """Append an element or string as child node.
         
@@ -146,14 +155,15 @@
         return Stream(self._generate())
 
 
-def _value_to_unicode(value):
-    if isinstance(value, unicode):
-        return value
-    return unicode(value)
-
 def _kwargs_to_attrs(kwargs):
-    return [(QName(k.rstrip('_').replace('_', '-')), _value_to_unicode(v))
-            for k, v in kwargs.items() if v is not None]
+    attrs = []
+    names = set()
+    for name, value in kwargs.items():
+        name = name.rstrip('_').replace('_', '-')
+        if value is not None and name not in names:
+            attrs.append((QName(name), unicode(value)))
+            names.add(name)
+    return Attrs(attrs)
 
 
 class Element(Fragment):
@@ -240,7 +250,7 @@
     def __init__(self, tag_, **attrib):
         Fragment.__init__(self)
         self.tag = QName(tag_)
-        self.attrib = Attrs(_kwargs_to_attrs(attrib))
+        self.attrib = _kwargs_to_attrs(attrib)
 
     def __call__(self, *args, **kwargs):
         """Append any positional arguments as child nodes, and keyword arguments
@@ -250,7 +260,7 @@
         :rtype: `Element`
         :see: `Fragment.append`
         """
-        self.attrib |= Attrs(_kwargs_to_attrs(kwargs))
+        self.attrib |= _kwargs_to_attrs(kwargs)
         Fragment.__call__(self, *args)
         return self