Index: gavo/formal/nevowc.py
===================================================================
--- gavo/formal/nevowc.py	(revision 8435)
+++ gavo/formal/nevowc.py	(working copy)
@@ -21,7 +21,7 @@
 from twisted.web import server
 from twisted.web import template
 
-from .twistedpatch import Raw
+from .twistedpatch import Raw, _ToStan, _NSContext
 
 NEVOW_NS = 'http://nevow.com/ns/nevow/0.1'
 TWISTED_NS = 'http://twistedmatrix.com/ns/twisted.web.template/0.1'
@@ -42,14 +42,14 @@
     pass
 
 
-class _ToStan(template._ToStan):
+class MyToStan(_ToStan):
     """A SAX parser unifying nevow and twisted.web namespaces.
 
     We also map invisible (nevow) to transparent (t.w).
     """
     def __init__(self, sourceFilename):
-        template._ToStan.__init__(self, sourceFilename)
-        self.prefixMap = template._NSContext()
+        _ToStan.__init__(self, sourceFilename)
+        self.prefixMap = _NSContext()
         self.prefixMap[NEVOW_NS] = "nevow"
         self.prefixMap[TWISTED_NS] = "nevow"
     
@@ -57,13 +57,13 @@
         # overridden to swallow attempts to map prefixes for our
         # standard namespaces
         if uri==NEVOW_NS or uri==TWISTED_NS:
-            self.prefixMap = template._NSContext(self.prefixMap)
+            self.prefixMap = _NSContext(self.prefixMap)
             return
         else:
             if prefix=="nevow":
                 raise Exception("You may not bind the nevow prefix"
                     " to a non-twisted or non-nevow URI")
-            template._ToStan.startPrefixMapping(self, prefix, uri)
+            _ToStan.startPrefixMapping(self, prefix, uri)
 
     def startElementNS(self, namespaceAndName, qName, attrs):
         # regrettably, we also need to map attribute namespaces;
@@ -107,7 +107,7 @@
         if ns==TWISTED_NS and name=='invisible':
             name = 'transparent'
 
-        return template._ToStan.startElementNS(self,
+        return _ToStan.startElementNS(self,
             (ns, name),
             qName,
             attrs)
@@ -123,7 +123,7 @@
     parser.setFeature(handler.feature_external_ges, 0)
     parser.setFeature(handler.feature_external_pes, 0)
 
-    s = _ToStan(getattr(fl, "name", None))
+    s = MyToStan(getattr(fl, "name", None))
     parser.setContentHandler(s)
     parser.setEntityResolver(s)
     parser.setProperty(handler.property_lexical_handler, s)
Index: gavo/formal/twistedpatch.py
===================================================================
--- gavo/formal/twistedpatch.py	(revision 8435)
+++ gavo/formal/twistedpatch.py	(working copy)
@@ -22,7 +22,24 @@
 from twisted.web import _stan 
 from twisted.web import template
 
+try:
+    # this is where we want to monkeypatch twisted.template
+    # in twisted 21+
+    from twisted.web import _template_util as _template_patchtarget
+except ImportError:
+    # this is where to monkeypatch in twisted 20
+    from twisted.web import template as _template_patchtarget
+_ToStan = _template_patchtarget._ToStan
+_NSContext = _template_patchtarget._NSContext
 
+
+def patchTwTemplate(name, obj):
+    """monkeypatches whatever module holds the twisted.web.template
+    definitions.
+    """
+    setattr(_template_patchtarget, name, obj)
+
+
 class _NoData(object):
     """A sentinel to signifiy no data was passed to clone.
     """
@@ -36,6 +53,8 @@
 class Tag(_StanTag):
     def __init__(self, tagName, attributes=None, children=None, render=None,
                  filename=None, lineNumber=None, columnNumber=None, data=None):
+        children = children or []
+        attributes = attributes or {}
         _StanTag.__init__(self, tagName, attributes, children, render, 
             filename, lineNumber, columnNumber)
         self.slotData = data
@@ -139,9 +158,10 @@
 
         return newtag
 
+
 # we have to monkeypatch a couple of places in twisted.web
 _stan.Tag = Tag
-template.Tag = Tag
+patchTwTemplate("Tag", Tag)
 _flatten.Tag = Tag
 
 
@@ -319,3 +339,5 @@
     res = tag.clone(True, newData)
     del res.attributes["nevow:data"]
     return res
+
+