then the base URL is considered to be the empty string and all
   embedded URLs within that document are assumed to be absolute URLs.




 
RFC 1808           Relative Uniform Resource Locators          June 1995


   It is the responsibility of the distributor(s) of a document
   containing relative URLs to ensure that the base URL for that
   document can be established.  It must be emphasized that relative
   URLs cannot be used reliably in situations where the document's base
   URL is not well-defined.

4.  Resolving Relative URLs

   This section describes an example algorithm for resolving URLs within
   a context in which the URLs may be relative, such that the result is
   always a URL in absolute form.  Although this algorithm cannot
   guarantee that the resulting URL will equal that intended by the
   original author, it does guarantee that any valid URL (relative or
   absolute) can be consistently transformed to an absolute form given a
   valid base URL.

   The following steps are performed in order:

   Step 1: The base URL is established according to the rules of
           Section 3.  If the base URL is the empty string (unknown),
           the embedded URL is interpreted as an absolute URL and
           we are done.

   Step 2: Both the base and embedded URLs are parsed into their
           component parts as described in Section 2.4.

           a) If the embedded URL is entirely empty, it inherits the
              entire base URL (i.e., is set equal to the base URL)
              and we are done.

           b) If the embedded URL starts with a scheme name, it is
              interpreted as an absolute URL and we are done.

           c) Otherwise, the embedded URL inherits the scheme of
              the base URL.

   Step 3: If the embedded URL's  is non-empty, we skip to
           Step 7.  Otherwise, the embedded URL inherits the 
           (if any) of the base URL.

   Step 4: If the embedded URL path is preceded by a slash "/", the
           path is not relative and we skip to Step 7.










 
RFC 1808           Relative Uniform Resource Locators          June 1995


   Step 5: If the embedded URL path is empty (and not preceded by a
           slash), then the embedded URL inherits the base URL path,
           and

           a) if the embedded URL's  is non-empty, we skip to
              step 7; otherwise, it inherits the  of the base
              URL (if any) and

           b) if the embedded URL's  is non-empty, we skip to
              step 7; otherwise, it inherits the  of the base
              URL (if any) and we skip to step 7.

   Step 6: The last segment of the base URL's path (anything
           following the rightmost slash "/", or the entire path if no
           slash is present) is removed and the embedded URL's path is
           appended in its place.  The following operations are
           then applied, in order, to the new path:

           a) All occurrences of "./", where "." is a complete path
              segment, are removed.

           b) If the path ends with "." as a complete path segment,
              that "." is removed.

           c) All occurrences of "/../", where  is a
              complete path segment not equal to "..", are removed.
              Removal of these path segments is performed iteratively,
              removing the leftmost matching pattern on each iteration,
              until no matching pattern remains.

           d) If the path ends with "/..", where  is a
              complete path segment not equal to "..", that
              "/.." is removed.