Typically the file format is 'imagemap' or 'htimage' dependant. But,
using HTTP/1.0 and a "good" IMAP backend there is no reason why you
shouldn't be able to say 'path/doc.html#page'.
Though most servers presently take 'Location:' headers and send you the
document rather than leaving it at that. If you run NCSA HTTPD there
are some straight forward things you can change to make it not
send the document but rather send just the reference and allow the browser
to refetch the document.