19.2. Where is process.html?
(Answered by Ed LaFrance & Kevin Walsh)
It is in the guts of Interchange. The [process] form action tells interchange to process the posted form vars according to the action set with mv_todo. The processing is not associated with any specific target page (though a page to display when processing is complete can be specified with mv_nextpage), so Interchange just builds a target URL that ends in an 'imaginary' page called 'process.html'.
There are other ways to handle a form post. For more information, see the Form Actions section Interchange Templates manual.
Basically, when you submit a <form> using the [process] tag, you get sent to the 'imaginary' process.html page. That page is derived from the page specified in the form's mv_nextpage CGI submission.