`--find-links=<path-or-url>`` or ``--[extra-]index-url=<path-or-url>``.

If a URL is supplied, it must be a ``file:`` URL. If a path is supplied to
the option, it is converted to a URL first. This returns:

* ``page_candidates``: Links listed on an HTML file.
* ``file_candidates``: The non-HTML file.
c