documents that have unsuitable base URLs.

2.1.  URL Syntactic Components

   The URL syntax is dependent upon the scheme.  Some schemes use
   reserved characters like "?" and ";" to indicate special components,
   while others just consider them to be part of the path.  However,
   there is enough uniformity in the use of URLs to allow a parser to
   resolve relative URLs based upon a single, generic-RL syntax.  This
   generic-RL syntax consists of six components:




 
RFC 1808           Relative Uniform Resource Locators          June 1995


      :///;?#

   each of which, except , may be absent from a particular URL.
   These components are defined as follows (a complete BNF is provided
   in Section 2.2):

      scheme ":"   ::= scheme name, as per Section 2.1 of RFC 1738 [2].

      "//" net_loc ::= network location and login information, as per
                       Section 3.1 of RFC 1738 [2].

      "/" path     ::= URL path, as per Section 3.1 of RFC 1738 [2].

      ";" params   ::= object parameters (e.g., ";type=a" as in
                       Section 3.2.2 of RFC 1738 [2]).

      "?" query    ::= query information, as per Section 3.3 of
                       RFC 1738 [2].

      "#" fragment ::= fragment identifier.

   Note that the fragment identifier (and the "#" that precedes it) is
   not considered part of the URL.  However, since it is commonly used
   within the same string context as a URL, a parser must be able to
   recognize the fragment when it is present and set it aside as part of
   the parsing process.

   The order of the components is important.  If both  and
    are present, the  information must occur after the
   .

2.2.  BNF for Relative URLs

   This is a BNF-like description of the Relative Uniform Resource
   Locator syntax, using the conventions of RFC 822 [5], except that "|"
   is used to designate alternatives.  Briefly, literals are quoted with
   "", parentheses "(" and ")" are used to group elements, optional
   elements are enclosed in [brackets], and elements may be preceded
   with * to designate n or more repetitions of the following
   element; n defaults to 0.

   This BNF also describes the generic-RL syntax for valid base URLs.
   Note that this differs from the URL syntax defined in RFC 1738 [2] in
   that all schemes are required to use a single set of reserved
   characters and use them consistently within the major URL components.







 
RFC 1808           Relative Uniform Resource Locators          June 1995


   URL         = ( absoluteURL | relativeURL ) [ "#" fragment ]

   absoluteURL = generic-RL | ( scheme ":" *( uchar | reserved ) )

   generic-RL  = scheme ":" relativeURL

   relativeURL = net_path | abs_path | rel_path

   net_path    = "//" net_loc [ abs_path ]
   abs_path    = "/"  rel_path
   rel_path    = [ path ] [ ";" params ] [ "?" query ]

   path        = fsegment *( "/" segment )
   fsegment    = 1*pchar
   segment     =  *pchar

   params      = param *( ";" param )
   param       = *( pchar | "/" )

   scheme      = 1*( alpha | digit | "+" | "-" | "." )
   net_loc     =  *( pchar | ";" | "?" )
   query       =  *( uchar | reserved )
   fragment    =  *( uchar | reserved )

   pchar       = uchar | ":" | "@" | "&" | "="
   uchar       = unreserved | escape