Both these solution seem to me quite advanced, Keith Moore's
idea with files seems simpler.
It's simpler but it doesn't work in lots of cases.
Question: Is it a common property of all Web browser, that
if you ask them to show a local file, and that file contains
relative HTTP URL-s, the web browser will look for those
as files in the same directory as the file you asked the
Web browser to show? Because that property of Web browsers
is the whole basis of Keith Moore suggested solution.
It depends on the nature of the relative URL. for example, if you have
a document that was originally http://host.dom/sample/foo.html
it might contain
<IMG SRC="/images/logo.gif">
i.e., try to call out an image using a relative URL that defaults to
the top level. If you then save this as
file:///usr/home/jpalme/foo.html
and open it, it will try to open the file "/images/logo.gif", i.e.,
not use the same source directory that "foo.html" was in.