Index: TwistedWords-0.5.0/twisted/words/xish/domish.py
===================================================================
--- TwistedWords-0.5.0/twisted/words/xish/domish.py	(revision 5107)
+++ TwistedWords-0.5.0/twisted/words/xish/domish.py	(revision 5108)
@@ -168,8 +168,7 @@
         self.prefixStack.pop()
 
 SerializerClass = _ListSerializer
-
-def escapeToXml(text, isattrib = 0):
+def escapeToXml(text, isattrib = 0,cache = {}):
     """ Escape text to proper XML form, per section 2.3 in the XML specification.
 
     @type text: L{str}
@@ -179,12 +178,21 @@
     @param isattrib: Triggers escaping of characters necessary for use as
                      attribute values
     """
+    if len(cache) > 1000000:
+        cache.clear()
+        
+    try:
+        return cache[text]
+    except:
+        pass
+    itext = text
     text = text.replace("&", "&")
     text = text.replace("<", "&lt;")
     text = text.replace(">", "&gt;")
     if isattrib == 1:
         text = text.replace("'", "&apos;")
         text = text.replace("\"", "&quot;")
+    cache[itext] = text
     return text
 
 def unescapeFromXml(text):