says dug:

The "protocol" section of the original post begins to describe how to standardize on which HTTP headers to use in which ways to do "simple http post/get" type interactions.

That has already been standardised in WebDAV. If your HTML editors (I'm guessing FrontPage) already support WebDAV, I'd try writing a WebDAV API to your server. Modules like HTTP::DAV or HTTP::Webdav might be of use.

We've done something similar where I work. We have content production software that runs under mod_perl with a SOAP::Lite interface. SOAP was an attractive options for us since it was relatively quick and painless to set up, and we wrote our own desktop application. We've been using it now for a year and a half.

Our desktop client application is written using Wx. We use an ActiveX control for WYSIWYG editing xml documents, and there's a syntax highlighed raw view using Wx::STC (Scintilla)

We'll probably add an FTP or WebDAV api so we can access our repositories from third-party applications. Our SOAP api is fine for our application but it's next to useless if we want to access our repositories from outside our app. Still, we can reuse the code in our FTP/WebDAV api.

I suggest using an open protocol from the beginning.