[Zope] Peculiar Zope WebDav Behavior

I open up a Zope 2.10.1 ZPT or DTML page in a webdav client, using Notepad or the Amaya web editor. Unfortunately, the DTML tags and ZPT attibutes get replaced with the substituted values. All I see in Notepad or Amaya are the rendered HTML that would get returned to the browser. Thus I cannot modify the ZPT or DTML page source, since the source is not visible. Is that intended behavior for Zope and WebDav? It seems kind of pointless. Is there a workaround? I don't object to using ZopeEdit, but I would prefer to use WebDav, since that is a general tool that is not specific to Zope. What is Zope/WebDav for if not for modifying the source (not the rendered HTML!) of ZPT and DTML objects?