How do I specify a specific combination of frames instead of the default document?
This is unfortunately not possible. When you navigate through a site using frames, the URL will not change as the documents in the individual frames change. This means that there is no way to indicate the combination of documents that make up the current state of the frameset.
The author can provide multiple frameset documents, one for each combination of frame content. These frameset documents can be generated automatically, perhaps being created on the fly by a CGI program. Rather than linking to individual content documents, the author can link to these separate frameset documents using TARGET="_top". Thus, the URL of the current frameset document will always specify the combination of frames being displayed, which allows links, bookmarks, etc. to function normally.