Added and documented the ability to control the parsing of a template as

XML or HTML with an 'is_html' property.  If this property doesn't exist,
the default content-type-sniffing behavior is used.

lib/python/Products/PageTemplates/PageTemplate.py

@@ -87,7 +87,7 @@
 HTML- and XML-based template objects using TAL, TALES, and METAL.
 """
 
-__version__='$Revision: 1.15 $'[11:-2]
+__version__='$Revision: 1.16 $'[11:-2]
 
 import os, sys, traceback, pprint
 from TAL.TALParser import TALParser
@@ -222,7 +222,9 @@ class PageTemplate(Base):
         self._v_warnings = parser.getWarnings()
 
     def html(self):
+        if not hasattr(getattr(self, 'aq_base', self), 'is_html'):
             return self.content_type == 'text/html'
+        return self.is_html
 
 class _ModuleImporter:
     def __getitem__(self, module):

lib/python/Products/PageTemplates/help/PageTemplate_Edit.stx

@@ -17,7 +17,15 @@ Edit View: Edit A Page Template
         'Title' -- Allows you to specify the Zope title of the template.
         
         'Content-Type' -- Allows you to specify the content-type that
-        will be given to renderings of this template.
+        will be given to renderings of this template.  Also, if the
+        content type is 'text/html' (the default) then the template is
+        assumed to contain HTML, not XML.  This affects both parsing
+        and rendering of the template, and can be overridden by giving
+        the template an 'is_html' property.
+
+        'Expand macros when editing' -- Allows you to turn the expansion
+        of METAL macros on or off.  This only affects viewing of the
+        source code, not rendering.
         
     Buttons and Other Form Elements