Issue List

   [under Windows] it's perfectly legal while on host "foo" to request
   file://server/folder/item.  On Win32, and on other systems, this
   requests the "item" stored in "folder" on the "server" machine.  On
   Win32, it magically works.

Actually, it is illegal but happens to work with Explorer, does not
work with Netscape under Windows, and may or may not work with other
Windows clients.

In general, the exact details of file URL handling is up to the client
you're using.  It's pretty uniform on UNIX systems but is NOT uniform
amongst Windows clients.  In particular, Netscape and Explorer handle
file URLs differently under Windows.  Here are some examples:

- Netscape correctly handles escapes (like file:///c%3A/ for the
  C drive), but Explorer does not.
- Netscape allows file:/// (which is empty), but Explorer does not.
- Explorer allows file:///\\remotehost\share\
              and file:////remotehost/share/, but Netscape does not.

I'm sure there are other differences.

[Windows Examples]
  	file://c:/temp/test.txt => open (FH, "c:/temp/test.txt");
  	file://c:\temp\test.txt => open (FH, "c:\\temp\\test.txt");
  	file://localhost/c:/temp/test.txt => open (FH, "c:/temp/test.txt");
  	file://remotehost/c:/temp/test.txt is not legal

Only the localhost example above is technically legal since host
portions of file URLs must be fully qualified domain names,
'localhost', or empty.  The second example is also illegal because a
mandatory '/' must follow the host portion.  For the details, see
RFC1738 (Uniform Resource Locators).

The first two examples can be made legal by writing them as
<file:///c:/temp/test.txt>.  This happens to work with both
Explorer and Netscape.  Again, be warned that it may or may not work
with other Windows clients.

As for UNC paths, I am not aware of a legal way to use them in file
URLs which works with both Netscape and Explorer.

RFC 2396 obsoletes 1738, which contained:

   ftp                     File Transfer protocol
   http                    Hypertext Transfer Protocol
   gopher                  The Gopher protocol
   mailto                  Electronic mail address
   news                    USENET news
   nntp                    USENET news using NNTP access
   telnet                  Reference to interactive sessions
   wais                    Wide Area Information Servers
   file                    Host-specific file names
   prospero                Prospero Directory Service

Of these, 'http' and 'mailto' are covered by their own RFCs now,
but 'ftp', 'news', 'telnet', 'file' should be re-issued. (It's OK
with me if we leave 'gopher', 'wais', and 'prospero' behind.)

'ftp' has never been properly specified, as actually implemented.
'news' should be updated to merge 'news' and 'nttp' according
to current practice, and 'file' needs a proper specification
that handles things like volume names on the windows platform and
suggests that other OS profiles should be developed for local
name mapping.

I've been working through the relative URI resolution
mechanism in RFC 2396, and I've spotted something which 
seems a little odd. The example resolution on p.29 for,

  ?y

from,

  http://a/b/c/d;p?q

is given as,

  http://a/b/c/?y

but as far as I can make out, the resolution algorithm
suggests the result ought to be,

  http://a/b/c/d;p?y

which is the result that was given in RFC 1808. It's
also the result that both Netscape 4 and IE 4 deliver.

Given that this would be an observable change in
behaviour between the two RFCs, I'm a little surprised 
that it wasn't flagged up as such if the change really 
was intended ...

Strangely enough, Sun's badly broken java.net.URL class 
_does_ give the result specified in 2396, which makes me 
suspect that something must be wrong ;-)

rfc2396 specifies a different browser behavior from rfc1808 in a particular
situation that I believe may be unintentional.  IE & Netscape implement the
rfc1808 behavior while Opera implements the rfc2396 behavior.  As appendix
G of rfc2396 makes no mention of this change, we would appreciate your
opinion on the matter.

In rfc1808, when the relative URL has no path component, but has a fragment
or a query, the client is supposed to skip step 6 of forming the absolute
URI.  In step 6, among other things, the base URI is stripped of all
characters beyond the final "/".

In rfc2396, when the relative URI has no path and has a fragment, it is
specified that processing should be stopped as no new document should be
loaded, but rather navigation within the document is specified.  This
change is explained in appendix G.

However, when there is no path component, but there is a query component,
processing continues.  The instruction to skip stripping the
post-final-/-characters is gone in rfc2396, which means that the final part
of the base URI is stripped and so the query is not performed on the same
page as was loaded (unless that page's URI ended with a "/".  Was this
change between rfc1808 and rfc2396 intended?

The following small php application illustrates the issue. You can run it
at http://www.media.mit.edu/opera/r-url.php.  You will note that Opera
(6.03) behaves very differently from Netscape and IE when executing this
page. With IE and Netscape, you can navigate within the application.  With
Opera, when you click on the links within the app, you get an index page of
the directory containing the app.

It is my belief that the final characters should *not* be stripped, and
that rfc2396 should be amended to skip the stripping in the case of a
relative URI with only a query component.

<html>
<head>
<title>Example application using empty path relative URLs</title>
</head>
<body>
<h4>Example application using empty path relative URLs</h4>
<?php if ($action=="here") { ?>
           Thank you for clicking here!<br><br>
<?php } else if ($action=="there") { ?>
           Hey, you weren't supposed to click there!<br><br>
<?php } ?>
Please click <a href="?action=here">here</a>.<br>
Please do not click <a href="?action=there">there</a>.<br>
<br>
Thank you.
</body>
</html>

Fixed by rewriting the algorithm as pseudocode and restoring the
original RFC 1808 behavior, with the example changed accordingly.

I tried to follow the algorithm in my implementation, but it gives
http://ab :-( 

I'm doing:

  Input: base: scheme = `http', authority = `a', path = `', query undefined
	 reference: `b'

  Step 1): path = `b'; scheme, authority, query are undefined
  Step 2): is a nop
  Step 3): scheme = `http'
  Step 4): authority = `a'
  Step 5): doesn't apply
  Step 6): a) gives buffer = `'
	   b) gives buffer = `b'
	   c) - g) don't apply
	   h) gives path = `b'
  Step 7): says `http' + `:' + `//' + `a' + `b'

I think there's a slight bug in the relative URI resolution algorithm in
RFC 2396.  Consider:

    Base URI = http://foo.com
    URI-reference = bar

As far as I can tell, the algorithm yields:

    http://foo.combar

This base URI is allowed according to the statement in section 5.2:

    Note that only the scheme component is required to be present in the
    base URI; the other components may be empty or undefined.

Here's a walk through the algorithm:

step 1:  parse reference (no problem)
step 2:  query/fragment not inherited from base (no problem)
step 3:  scheme inherited from base (no problem)
step 4:  authority inherited from base (no problem)
step 5:  reference is not absolute (no problem)
step 6a: base URI's path (which is undefined) is copied into buffer
         (So the buffer is empty?  This may be part of the problem.)
step 6b: "bar" is appended to the buffer (which now contains "bar")
step 6c: remove ./ (no-op)
step 6d: remove trailing . (no-op)
step 6e: remove segment/../ (no-op)
step 6f: remove trailing segment/.. (no-op)
step 6g: check for leading .. (none found)
step 6h: buffer is the new path ("bar")
step 7:  result = ""
         append "http"
         append ":"
         append "//"
         append "foo.com"
         append "bar"
         (No check for initial slash, this may be part of the problem.)
         return "http://foo.combar"

Presumably the desired absolute URI is http://foo.com/bar.  Possible
ways to achieve this include:

 1) Alter step 6a to initialize the buffer to "/" if the base URI has no
    path.

 2) Alter step 7 to insert a slash before any path that does not begin
    with a slash (including an empty path).

 3) Alter step 7 to insert a slash before any path that begins with a
    non-slash (but not before an empty path).

I think proposals 1 and 2 are equivalent, but I haven't considered it
carefully.  Proposal 3 gives a different result if the reference is "./"
and the base URI has no path.  Proposal 1 looks the cleanest to me.

I guess step 6a should be

      a) All but the last segment of the base URI's path component is
         copied to the buffer.  In other words, any characters after the
         last (right-most) slash character, if any, are excluded.
         If the base URI's path component is the empty string, then
         a single slash character ("/") is copied to the buffer.

Fixed as described above.

If you've already done any server-side commands, you should take a look at
the current specification and consider re-implementing them if you want any
clients to use them.

  http://www.wu-ftpd.org/rfc/draft-ietf-ftpext-mlst-09.txt

or

  ftp://ftp.ietf.org/internet-drafts/draft-ietf-ftpext-mlst-09.txt

MIME types are a "Standard Fact".  They may or may not be present.  If
present, they must conform to the IANA-approved list of type names.

While you're at it, you should notice that language negotiation is, too
some extent, also possible.  For this, in addition to the MLST draft, you
should also take a look at RFC 2640, "Internationalization of the File
Transfer Protocol".

The site

  http://www.wu-ftpd.org/rfc/

contains a complete list of the FTP RFCs.  (Well, nearly complete.  I'm
told there's another URL RFC I should include.)  If you don't want to
browse the site, or have a local mirror of the RFCs, the complete list of
current RFCs which define the FTP is: 959, 1123, 1579, 1635, 1738, 1808,
2228, 2415, 2428, 2577 and 2640.

The MLST draft just underwent a major change (splitting a feature out for a
separate draft).  Other than that, it is fairly mature and should be
progressing to submission to the RFC Editor.  The other FTP-related IETF
drafts have, by now, expired and are not expected to progress to
submission.

I have recently spent a considerable amount of time studying the URI spec
[1]	http://www.ietf.org/rfc/rfc2396.txt
and I discovered, somewhat to my surprise, that it
defines the terms "URI reference" and "absolute URI" very precisely,
but
        (a) it doesn't define the term "URI", syntactically (!!!)
and
        (b) it doesn't give a term for an
absolute-URI-with-optional-fragment-id , i.e. the result of combining
a URI reference with an absolute URI.

This is pretty awkward, since an absolute-URI-with-optional-fragment-id is
really what we meant when we wrote "URI reference" in:

"An XML namespace is a collection of names, identified by a URI
reference"
-- http://www.w3.org/TR/1999/REC-xml-names-19990114/#sec-intro

We used "URI reference" because "absolute URI" excludes fragment identifiers,
and we wanted
	http://example.net/#vocab
to be a valid namespace identifier.

But
	../xyz/
isn't a namespace identifier, until you combine it with a base absoluteURI.

Another example:

"The locator attribute provides a URI-reference that identifies a remote
resource (or sub-resource)"
-- http://www.w3.org/TR/1999/WD-xlink-19991220/#Local Resources for an
Extended Link

URI-references don't identify remote resources; absoluteURIs do. The
"or sub-resource" makes it clear that the author intends to allow #fragids.
So again, what's needed is a term for absolute-URI-with-optional-fragment-id.

It was called fragmentaddress in RFC1630.

If formal systems float your boat, you can take a look at my formalism
of this stuff in larch:
        http://www.w3.org/XML/9711theory/URI
        http://www.w3.org/XML/9711theory/URI.html (HTML version with
                nasty hacks for math symbols)
        http://www.w3.org/XML/9711theory/URI.lsl (original ascii LSL version)

part of
        "Specifying Web Architecture with Larch"
        http://www.w3.org/XML/9711theory/

which gives pointers explaining larch etc.

I used the term URIwf for absolute-URI-with-optional-fragment-id, and
I used absoluteURI and URI_reference with their rfc2396 meanings.

absolute-URI-reference has been added to the section on URI reference
and the ABNF.

I have an observation regarding section -- "C. Examples of Resolving
Relative URI References" -- within this document.

The document cites that given the well-defined base URI of

    http://a/b/c/d;p?q

relative URI

    ?y

would be resolved as follows:

    http://a/b/c/?y

By my interpretation from the BNF, a query can exist as either

    relativeURI = ( net_path | abs_path | rel_path ) [ "?" query ]

or

    hier_part = ( net_path | abs_path ) [ "?" query ]

Since net_path, abs_path and rel_path must each be a least one character in
length, I believe that the example "?y" is not a valid URI because no
characters proceed the question mark (?).

     Appendix C shows an example of a relative URI Reference of "?y" with 
respect to the base URI "http://a/b/c/d;p?q".  However, according to the 
collected syntax that appears in Appendix A, "?y" doesn't appear to be a 
valid relative URI reference.  The syntactic category URI-reference must 
begin with an absoluteURI, a relativeURI or a pound sign.  An absoluteURI 
begins with a scheme, which cannot begin with a question mark; a 
relativeURI begins with a net_path or abs_path, both of which begin with a 
slash, or with a rel_path.  A rel_path begins with a non-empty 
rel_segment, which again cannot begin with a question mark.

Section C.2 mentions an empty reference, but the
formal syntax does not provide for that. There are
several possible changes to the formal syntax which
would permit it, e.g. change 1* to * in the
definition of rel_segment, which would permit an
empty rel_path and therefore relativeURI (however,
it would then permit a relativeURI consisting of
"?" query, which might not be desired).
Alternatively, the entire RHS of the relativeURI
definition could be bracketed, i.e. made optional,
which would permit an empty relativeURI without
permitting a lone delimited query.

I don't even remember making this change, but it was broken
when draft-fielding-uri-syntax-02.txt changed from

      rel_path      = [ path_segments ] [ "?" query ]

to (in 03):

      rel_path      = rel_segment [ abs_path ]

      rel_segment   = 1*( unreserved | escaped |
                          ";" | "@" | "&" | "=" | "+" | "$" | "," )

Fixed by making the path optional in the ABNF:

2396:

   relativeURI   = ( net_path | abs_path | rel_path ) [ "?" query ]
   hier_part     = ( net_path | abs_path ) [ "?" query ]

draft-00:
   relative-URI  = [ net-path / abs-path / rel-path ] [ "?" query ]
   hier-part     = [ net-path / abs-path ] [ "?" query ]

When we update RFC 2396, I suggest we add an introductory paragraph
explaining that the term "URI" is used ambiguiously in the community
to mean "a URI reference" (corresponding to the URI-reference BNF entity)
or "an absolute URI", and that for this reason, the term "URI" itself
is not defined in the document.

I'd probably fix the Abstract correspondingly, e.g.,

"Informally, a Uniform Resource Identifier is a compact string...."

so that people don't think that the abstract is normative.

It seems to me, in considering points raised in the "Are URI-References bound 
to resources?" thread, that some subtleties might be a bit more clear if  
changes along the following lines were made to RFC 2396 (i.e. in a future 
revision of that doc, if any)..

4. URI References

   The term "URI-reference" is used here to denote the common usage of a
       ^^^^                 ^^^^^^^^^^^^^^^       ^
     production                 (delete)          s

   resource identifier.  A URI reference may be absolute or relative,
                       ^
       The term "URI reference" is a casual (i.e. natural
       language) description for artifacts that are parsable
       using the "URI-reference" production.


   and may have additional information attached in the form of a
   fragment identifier.  However, "the URI" that results from such a
   reference includes only the absolute URI after the fragment
   identifier (if any) is removed and after any relative URI is resolved
   to its absolute form.  Although it is possible to limit the
   discussion of URI syntax and semantics to that of the absolute
   result, most usage of URI is within general URI references, and it is
   impossible to obtain the URI from such a reference without also
   parsing the fragment and resolving the relative form.

      URI-reference = [ absoluteURI | relativeURI ] [ "#" fragment ]
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                               (delete)


add:             URI = absoluteURI | relativeURI

add:   URI-reference = [ URI ] [ "#" fragment ]

                                  .
                                  .
                                  .
 
It seems to me that the above suggested re-write of the URI-reference 
production, and the additions to the preceding text, would make it easier and 
clearer to talk about "URI" artifacts and "URI-reference" artifacts and their 
different abstract semantics.

Also, the _term_ "URI reference" isn't defined prior to section 4 (wherein it 
is only tangentially defined, imho). Terms that are also used in sections 
prior to section 4 whose explicit definition would help the document convey 
it's rather abstract notions to the reader are: "document" and "reference". 
Explicitly defining how those terms are used and what their semantics are in 
the context of URI and URI-reference artifacts are, would be immensely helpful 
to readers.

I found that according to BNF of RFC 2396 "URI Generic Syntax", the
following string is accepted as a valid URI.

"http://12345.678/"

I assumed this should be rejected because substring "12345.678" does not
match hostname production of BNF.

However, actually this string is accepted by the following derivation.

   absoluteURI
 - scheme ":" hier_part
 - "http" ":" abs_path
 - "http:" "/" path_segments
 - "http:/"    segment "/" segment "/"
 - "http:/"    *pchar  "/" *pchar "/"
 - "http:/"            "/" "12345.678" /"
 - "http://12345.678/"

As you see, the fact that segment is nullable makes net_path
production meaningless.

Is this the intention of authors? Or should it be considered as a bug in
BNF? If so, is it appropriate to fix this bug by changing segment as
follows?

   segment = 1*pchar *( ";" param )

That URI is valid (maybe not for http, but for the URI syntax in general).
The generic syntax requires that the components be extracted first in
order to disambiguate these cases (the greedy rule).  Only after the
components are extracted can the syntax of those components be tested
for correctness.

Is "foo://" a legal URI in RFC 2396? If so, is the path componebnt "//" or 
empty?

On the one hand, "//" doesn't parse as net_path so it parses unambigously 
as an abs_path, so the disambiguating rule in 4.3 is arguably not 
applicable. This would suggest it is legal, and the path component is "//".

On the other hand, if you use the regex in appendix B, the // will be 
treated as an empty authority component (which is not legal) rather than as 
a path component.  Maybe the regex should use

//([^/?#]+)

instead of

//([^/?#]*)

so that the regex splits things consistently with the grammar.

Alternatively, reg_name could be changed so that it matches the empty 
string, so that // would parse as a net_path, and hence there would be an 
ambiguity to which 4.3 could be applied, and the existing regex would be 
consistent.

I just looked at this again, and an empty authority is fine;
it turns out to look like an empty 'server', rather than an empty 'regname'.

      server        = [ [ userinfo "@" ] hostport ]

So "//" does parse as net_path, and the regex in appendix B is fine.

RFC 2396 contains the following BNF for the host part of a URI:

       host          = hostname | IPv4address
       hostname      = *( domainlabel "." ) toplabel [ "." ]
       domainlabel   = alphanum | alphanum *( alphanum | "-" ) alphanum
       toplabel      = alpha | alpha *( alphanum | "-" ) alphanum
       IPv4address   = 1*digit "." 1*digit "." 1*digit "." 1*digit
       port          = *digit

Typical implementations use // and / to locate the hostport part, and
break things apart and use gethostbyname() to resolve the IP address.
Gethostbyname() has quite a different syntax, however, allowing IP
addresses such as

    http://63.197.151.31/  (as above; class C syntax)
    http://63.197.151.037/ (leading zero means octal, but still within
                            the BNF of above)
    http://63.197.38687/   (two-dot notation; class B syntax)
    http://63.12949279/    (one-dot notation; class A syntax)
    http://1069913887/     (numeric IP syntax)

and of course all combinations of above, including

    http://07761313437/    (octal)
    http://000000077.0000000305.000000000227.00000000037/ (leading zeros)

I have two points.  First, the implementations are out of sync with the
specification.  Does this matter?  Secondly, one can argue that the
implied semantics of the BNF given above for a four-dot representation
is a decimal interpretation, where the implementations use octal of any
component of the IP address begins with a leading zero (unlike what happens
for the port, where http://63.197.151.31:0000000080/ accesses port 80).

http://www.ietf.org/rfc/rfc2732.txt

IPv6 literals have been added to the list of possible identifiers
for the host portion of a server component, as described by RFC 2732,
with the addition of "[" and "]" to the reserved, uric, and
uric-no-slash sets.  Square brackets are now specified as reserved
for the authority component, allowed within the opaque part of an
opaque URI, and not allowed in the hierarchical syntax except for
their use as delimiters for an IPv6reference within host.  In order
to make this change without changing the technical definition of
the path, query, and fragment components, those rules were redefined
to directly specify the characters allowed rather than continuing
to be defined in terms of uric.

Since RFC 2732 defers to RFC 2373 for definition of an IPv6 literal
address, which unfortunately has an incorrect ABNF description of
IPv6address, I created a new ABNF rule for IPv6address that matches
the text representations defined by Section 2.2 of RFC 2373.
Likewise, the definition of IPv4address has been improved in order to
limit each decimal octet to the range 0-255.

The XML schema anyURI simple type allows any string which after escaping 
disallowed characters as described in Section 5.4 of XLink is a URI 
reference as defined in RFC 2396, as amended by RFC 2732. This raises the 
question of what exactly it takes for an implementation to check this.

Putting on one side the RFC 2732 amendments (and the consequent 
non-escaping of square brackets by the XLink algorithm), I believe it's 
very simple.  To check a string, do the following:

1. Check that every % is followed by two hex digits.

2. Check that there is at most one # character in the string.

3. If the string contains a ":" character that precedes all "/", "?" and 
"#" characters, then the string is an absolute URI and the substring 
preceding the first such colon must match the regex [a-zA-Z][-+.a-zA-Z0-9]*.

4. If the string is an absolute URI (as in 3), the the first colon must not 
be immediately followed by a # or the end of the string. (For example, 
"foo:" and "foo:#bar" are illegal.)

I think that's it. It's not straightforwatd to deduce this from RFC 2396 
and XLink, so I am not 100% confident.

RFC 2732 seems to radically complicate things. It adds "[" and "]" to the 
set of reserved characters and removes them from unwise. This has the 
effect of allowing square brackets in the query component and the fragment 
component.  The first problem arises with the path component.  Since pchar 
is defined in RFC 2396 as

unreserved | escaped |
  ":" | "@" | "&" | "=" | "+" | "$" | ","

it is unaffected by RFC 2732 and thus square brackets are not allowed in 
the path component.  This is a little bit strange, since intuitively pchar 
is an any uric other than "/", "?" and ";", but it complicates checking 
only a little.

The big problem is with the authority component.  Before RFC 2732, checking 
generic URI syntax did not require any complex parsing of the authority 
component, because an authority can be a reg_name, which allows one or more 
of any uric other than "/" and "?".  The problem is that because reg_name 
is defined as:

1*( unreserved | escaped | "$" | "," |
    ";" | ":" | "@" | "&" | "=" | "+" )

it is unaffected by RFC 2732.  Thus square brackets are not allowed to 
appear arbitrarily in the authority component, but can only appear if the 
authority component matches the server production (as amended by RFC 2732). 
This means that a generic URI checker now has to do a complex parse of the 
authority component.

This seems completely at variance with the intent of section 3.2.1 of RFC 
2396:

"The structure of a registry-based naming authority is specific to the URI 
scheme, but constrained to the allowed characters for an authority 
component."

I would therefore suggest at a mininum that RFC 2732 should be fixed to 
allow "[" and "]" in reg_name.  I also think it would be cleaner and more 
in harmony with RFC 2396 to also allow them in the path component.  In 
terms of the BNF I would suggest introducing an other_reserved symbol:

other_reserved = "&" | "=" | "+" | "$" | "," | "[" | "]"

Then in each place in RFC 2396 replace occurrences of

 "&" | "=" | "+" | "$" | ","

(specifically in uric_no_slash, rel_segment, reg_name, userinfo, pchar, 
reserved) by a reference to other_reserved. I believe this would also make 
the BNF in RFC 2396 easier to understand.

I report what I suspect to be an error in RFC 2732 which updates RFC 2396.

I suspect that 'uric_no_slash' set of characters has been forgotten
in the list of changes made to the URI generic syntax by RFC 2732.

Here is my line of argument:

Since:

    1. The set 'uric_no_slash' stands for "same as 'uric' BUT without slash";

    2. The set 'uric' is defined as:

        uric          = reserved | unreserved | escaped

    3. Slash ("/") is part of 'reserved' set;

    4. Set of 'reserved' characters is modified in RFC 2732.

As a result, point (3) of section 3. in RFC 2732 should be:

   (3) Add "[" and "]" to both the set of 'reserved' characters and
   the 'uric_no_slash' set:

      reserved      = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "+" |
                      "$" | "," | "[" | "]"
      uric_no_slash = unreserved | escaped | ";" | "?" | ":" | "@" |
                      "&" | "=" | "+" | "$" | "," | "[" | "]"

   and remove them from the 'unwise' set:

      unwise        = "{" | "}" | "|" | "\" | "^" | "`"

This indeed appears to be an oversight, thanks. Larry Masinter is thinking about
combining these two RFCs in their next update so this needs to go on his list. 

I agree that this is an error in RFC 2732, and should be
folded in when we merge RFC 2732 with RFC 2396. We would
need two independent interoperable implementations of
RFC 2732 (with ipv6 addresses), though.

Adding square brackets to uric_no_slash is fine, since it only affects
the opaque URI syntax.  However, adding it to the other places that
James Clark suggested would allow square brackets to be used anywhere,
which is simply unwise (and why they were not allowed at all before).
I can understand why IPv6 chose square brackets as delimiters, but
allowing them in path, query, and fragment would cause too many
interoperability issues with deployed systems.

IPv6 literals have been added to the list of possible identifiers
for the host portion of a server component, as described by RFC 2732,
with the addition of "[" and "]" to the reserved, uric, and
uric-no-slash sets.  Square brackets are now specified as reserved
for the authority component, allowed within the opaque part of an
opaque URI, and not allowed in the hierarchical syntax except for
their use as delimiters for an IPv6reference within host.  In order
to make this change without changing the technical definition of
the path, query, and fragment components, those rules were redefined
to directly specify the characters allowed rather than continuing
to be defined in terms of uric.

Section 3.4, "Query Component", of RFC2396 (URI syntax) refers to the 
"/" character as being reserved.

Reserving this character creates an inconsistency for some of today's 
web servers, which confuse part of the Query Component as being part of 
the Path Component when the "/" character is present in the Query
Component.

The "/" character should only be permitted in the Path Component of a 
URI, and elsewhere in the URI it should be escaped by using it's hex
value.

This is not an error in the spec, though it could be useful as a note
in future revisions.  The specification cannot disallow characters that
commonly do appear in a URI query string, even if it is inadvisable
for them to be used.  That is why they are listed as reserved in that
context (i.e., should not be used unencoded except when the reserved
meaning is intended).

(1) RFC2518 (WebDAV) is based on XML + namespaces and has chosen to use the
namespace name "DAV:" to identify it's elements. Note that "DAV:" *is* a
properly registered URI scheme)

(2) The XML namespaces recommendation says that an XML namespace is
identified by a URI reference as defined in RFC2396.

(3) RFC2396 gives the following grammar for absolute URIs:

absoluteURI   = scheme ":" ( hier_part | opaque_part )
opaque_part   = uric_no_slash *uric

"DAV:" doesn't seem to be a valid "opaque_part", because "opaque_part" MUST
start with "uric_no_slash", thus it may not be empty.

(4) I became aware of this mismatch when trying to develop a RELAG NG schema
for WebDAV. James Clark's JING validator rejects the namespace name "DAV:"
as invalid URI. So this has become a real-world problem (maybe it was "just"
academic before).

will fix BNF

Fixed by making the path optional in the BNF:

2396:

   relativeURI   = ( net_path | abs_path | rel_path ) [ "?" query ]
   hier_part     = ( net_path | abs_path ) [ "?" query ]

draft-00:
   relative-URI  = [ net-path | abs-path | rel-path ] [ "?" query ]
   hier-part     = [ net-path | abs-path ] [ "?" query ]

    I'm gathering you want resolveURI to take any URI ref and return an
    absolute URI reference.

    Instead, what I would do is define resolveURI as a function that
    takes any URI-reference-up-to-but-not-including-the-fragment-id and
    returns the appropriate absolute URI.  The fragment id part is never
    sent to resolveURI and is always re-appended to what resolveURI returns.

I based my implementation on the example algorithm in Section 5.2. Despite
being titled "Resolving Relative References to Absolute Form", it does cover
non-relative URI references (see step 3). Step 2 covers the case where the
URI reference is the empty string or just a fragment identifier. In that
case, it states the the reference is a "reference to the current document
and we are done".

Hmm. Looking at this paragraph again, I now think that it might be slightly
flawed. It says "and we are done". It doesn't mention that the fragment
identifier, if present, should be appended to the URI of the current
document.

    In this model, if resolveURI is handed a null string, it just returns
    a null string and the calling code would know to use the fragment id
    to access into the current resource without anyone having to talk
    about a document URI (which may not exist if, say, you're working
    on some in-memory view of a dynamic document--and even if there is
    such a URI, you wouldn't want to use the URI to do a fetch of the
    document that is the current one anyway).

I'm fairly certain that my implementation will produce the correct result as
would the model that you suggest above. It passes all of the tests in
Appendix C. I'm actually working on an RDF parser (in XSLT) so am not
fetching any resources but I do need to convert all URI references to their
absolute form and would like that encapsulated into a single function.

Fixed by rewriting the algorithm as pseudocode.

I believe that there is a discrepancy between 3.2.2
and the DNS specifications referenced there. The
definition in 3.2.2 for hostname is:

      hostname      = *( domainlabel "." ) toplabel [ "." ]
      domainlabel   = alphanum | alphanum *( alphanum | "-" ) alphanum
      toplabel      = alpha | alpha *( alphanum | "-" ) alphanum

That permits a lone toplabel as the hostname, which
could of course apply to the URI "http://localhost".
The definitions of domainlabel and toplabel appear
to be consistent with the DNS specifications, as
amended by RFC 1123 (but with the proviso that the
length limits specified by DNS are missing), but I
believe that there are some problems with the
definition of hostname in terms of those tokens. In
particular, the semantics of the above example differ
from what is implied by the name "toplabel". The
syntax permits URIs like "http://localhost." and
"http://edu", which don't seem quite right, and it
forbids "http://1xyz", where "1xyz" is a valid
unqualified host name (in the DNS sense). I believe
that a more consistent (with DNS and the text of sect.
3.2.2) definition of hostname syntax would be:

      hostname      = domainlabel [ *( "." domainlabel ) "." toplabel [ "." ] ]

Does that seem reasonable?

The grouping within the specifications of domainlabel
and toplabel could be clarified by parenthesization:

      domainlabel   = alphanum | ( alphanum *( alphanum | "-" ) alphanum )
      toplabel      = alpha | ( alpha *( alphanum | "-" ) alphanum )

or equivalently but more compactly as:

      domainlabel   = alphanum [ *( alphanum | "-" ) alphanum ]
      toplabel      = alpha [ *( alphanum | "-" ) alphanum ]

Changed to reflect all of the suggestions:

   hostname      = domainlabel [ qualified ]
   qualified     = *( "." domainlabel ) [ "." toplabel [ "." ] ]
   domainlabel   = alphanum [ 0*61( alphanum | "-" ) alphanum ]
   toplabel      = alpha    [ 0*61( alphanum | "-" ) alphanum ]
   alphanum      = ALPHA / DIGIT

This is a comment about RFC 2396 that I have been actioned to send on behalf
of the W3C RDF Core Working Group [1]

The key issue concern resolving same document references and/or resolving
against non-hierarchical URIs.

These have been causing us difficulty in using xml:base

As one of our deliverables we produce test cases [2].

A summary table of our URI resolution problems is as follows;
the answers we have agreed are in the attached HTML file.


EASY:
a "http://example.org/dir/file"      "../relfile"
b "http://example.org/dir/file"      "/absfile"
c "http://example.org/dir/file"      "//another.example.org/absfile"

GETTING HARDER:
d "http://example.org/dir/file"      "../../../relfile"
e "http://example.org/dir/file"      ""
f "http://example.org/dir/file"      "#frag"

MASTER CLASS:
g "http://example.org"               "relfile"

h "http://example.org/dir/file#frag" "relfile"
i "http://example.org/dir/file#frag" "#foo"
j "http://example.org/dir/file#frag" ""

k "mailto:Jeremy_Carroll@hp.com"     "#foo"
l "mailto:Jeremy_Carroll@hp.com"     ""
m "mailto:Jeremy_Carroll@hp.com"     "relfile"


We have reached consensus on and approved all these tests except for the
last which some of us consider an error and others resolve as indicated in
the html file.

The rationales for our views are approximately as follows:

d "http://example.org/dir/file"      "../../../relfile"

[[[RFC2396
   In practice, some implementations strip leading relative symbolic
   elements (".", "..") after applying a relative URI calculation, based
   on the theory that compensating for obvious author errors is better
   than allowing the request to fail.
]]]
Not permitted in RDF/XML.

e,f,i,j,k,l
Base does apply to same document references in RDF/XML

g
Failure to insert / is a bug with RFC 2396

h,i,j
Strip frag id from base uri ref before resolving.
Notice j is particularly surprising.

k,l
Same document reference resolution even works for non-hierarchical uris.

m
- no consensus


The test suite is structured as follows:

The positive tests on the test cases web site show a usage of xml:base in
RDF/XML and the resolution of that usage in terms of the RDF graph produced
(with absolute URI ref labels). Each test consists of two files, an RDF/XML
document and an n-triple file (substitute .rdf with .nt in the URL), being a
list of the edges of the graph.

The negative test case shows possibly illegal usage of xml:base in RDF/XML.

[1] http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Apr/0008.html

[2] http://www.w3.org/2000/10/rdf-tests/rdfcore/xmlbase/

I do not recall the RDF Core WG having resolved a justification of the
decision in favour of the these test cases. Hence I will give my own
justification.

First:
The actual decisions of the RDF Core WG reflect what 'same document
references' mean within an RDF/XML document within the scope of an xml:base
attribute. Primarily the WG decisions reflect the meaning of RDF/XML rather
than XML Base of RFC 2396. However, these decisions do point to weaknesses
in RFC 2396.

The RDF Core WG has consistently (with or without xml:base) interpreted all
uri references as absolute uri references. The decisions clarify that when
the normal uri resolution mechanisms deliver a same document reference, we
form the absolute uri ref using the currently in scope xml:base uri.

Second:

The definition of same-document references is unfortunately focussed on
browsing:
[[[
4.2. Same-document References

    A URI reference that does not contain a URI is a reference to the
    current document.  In other words, an empty URI reference within a
    document is interpreted as a reference to the start of that document,
    and a reference containing only a fragment identifier is a reference
    to the identified fragment of that document.  Traversal of such a
    reference should not result in an additional retrieval action.
    However, if the URI reference occurs in a context that is always
    intended to result in a new request, as in the case of HTML's FORM
    element, then an empty URI reference represents the base URI of the
    current document and should be replaced by that URI when transformed
    into a request.
]]]

line 3 "start of that document" is meaningless for an RDF document.
RDF is a graph and is not a linear structure.

line 6 "no additional retrieval action" All URIrefs in RDF are absolute, and
none are retrieved accept when the application content "is always intended
to result in a new request".

The RDF Core is trying to clarify which absolute URI ref corresponds to a
same document ref.

line 9 The answer, at least for empty same document refs, it is the "base
URI".

We discover what a base URI is in section "5.1 Establishing a Base URI"
[[[
5.1. Establishing a Base URI

   The term "relative URI" implies that there exists some absolute "base
   URI" against which the relative reference is applied.  Indeed, the
   base URI is necessary to define the semantics of any relative URI
   reference; without it, a relative reference is meaningless.  In order
   for relative URI to be usable within a document, the base URI of that
   document must be known to the parser.
]]]

I note that the algorithm in
5.2. Resolving Relative References to Absolute Form
amongst its defects, does not implement line 9 of section 4.2.

Once we are dynamically changing the xml:base from one element to the next,
we are outside the design bounds of RFC 2396.

If we consider only documents with a single xml:base on their outermost
elements, then as far as RDF goes, the resolution of the same document test
cases is consistent with section 4.2 of RFC 2396.  A same document
reference, like any uri ref, in an RDF file means an absolute URI ref. The
absolute URI ref is formed by taking "the base URI" of the document, as
suggested in line 9 of 4.2. The fragment part if taken from the same
document reference.

The bad news:

In fact, "the same document" in fragment-only relative references should be
taken even more locally and particularly than "the URI from which this
representation was recovered."  The latter reading is inadequate, an error. 
It should be read as "this representation."  So the type is known, and with
it the semantics of #fragment references.  Without recourse to _even_ the
URI from which it was recovered.  As Paul suggested.  For hyperlinks with
goTo semantics, where the absolute URI equivalent of the reference is
unnecessary, it is moot and therefore not defined.  The best available
absolute reference (nearest to equivalent) would be base-ified using the
URI from which this representation was recovered, but that question has
no need and no standing in the case of following hyperlinks in browsing
the same "recovered representation."  There is no general answer, absent
a universal document type (see next).

The good news:

The semantics of #fragment in "the current document" is governed by the
_type_ of the recovered represetation of the URI accessed.  So for RDF
to apply the semantic constraint that a #fragment reference is equivalent
to a given absolute URI -- within a representation which belongs to a type
which by its type definition is bound to the constraints of the RDF
model -- is entirely within the purview of the specification of the
RDF model and the languages in which it is represented.

This violates the universality goal that any URI-reference can be used
in any place a URI-reference can be used, but that is a different matter. 
This is also violated by having some references take anyURI and others
limited to IDREF in the same document.  The RDF restriction to
absolute-URI-reference senses for fragment-URI-reference signs does not
violate RFC-2396, at least.  This is just that the RDF model only admits
of 'absolute' references.  So references in any syntax binding of the
RDF model will only contain 'absolute' URI-references.

First: the problem RDF is trying to solve.  The current RDF specs have 
encouraged the use of the following idiom:

   <rdf:Description rdf:about="#foo">
     ...

The value of the rdf:about attribute is turned into an absolute URI 
reference by concatenating the '#foo' with the URI of the containing document.

This causes problems.  Folks copy the file from the web to their hard drive 
so they can work on it in a plane, and the uri changes to something like 
file:c:\temp\....rdf and this is really useless for rdf users.  Or folks 
wish to include RDF in say a message protocol where  there is no base uri 
of the document.
This is the cause of one of, if not the, most frequent newbie problem with 
DAML that we see on jena-dev.

So we are looking for a way to retain this convenient syntax, but have the 
uri's produced not change when the file is copied or mirrored.

To appreciate what is happening here, we need to look at a semi-fictional 
RDF processing pipeline:


input xml document --
          xml parser -- rfc2396 processor -- rdf parser -- rdf graph

We start with an xml document and end up with a datastructure.  The 
datastructure is not a DOM; its not a representation of an xml 
document.  It is as far as xml is concerned, an application data structure.

For each value of an rdf:about attribute, the rfc2396 processor outputs 
either an absolute URI or a same document reference.  The absolute URI is 
processed according to RFC2396.  Same document references are recognised 
according to RFC 2396.

All is in conformance with rfc 2396 at this point.

Now the RDF parser comes in to play and it is required to transform the 
value of each rdf:about attribute into an absolute uri reference.  If the 
RFC 2396 processor has produced an absolute uri reference, it need do 
nothing.  If however, it is a same document reference, then, just as a 
browser will handle same document references specially, so does RDF.  It 
transforms the same document reference into an absolute URI according to an 
algorithm defined by the RDF specs.  The mimetype of an rdf document will 
be text/xml+rdf.  As far as xml base and rfc 2396 are concerned, this is 
application code over which they have no say.

What I have tried to do here is to position RDF as an application built on 
top of XML and to suggest that XML should not be allowed to express 
constraints on how applications process it.

There is a deal of sophistry in this argument :( but RFC 2396 doesn't 
really meet our needs.  Are there any plans to update/refine it in the near 
future?

On RFC 2732 Page 1 / Point 2
you can find this example:

http://[::192.9.5.5]/ipng

1. When I take a look on the RFC 2373 logic (Page 21/Appendix B):

      IPv6address = hexpart [ ":" IPv4address ]
      IPv4address = 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT

      IPv6prefix  = hexpart "/" 1*2DIGIT

      hexpart = hexseq | hexseq "::" [ hexseq ] | "::" [ hexseq ]
      hexseq  = hex4 *( ":" hex4)
      hex4    = 1*4HEXDIG

2. When I take a look on the RFC 2732 logic update (Page 2):

      host          = hostname | IPv4address | IPv6reference
      ipv6reference = "[" IPv6address "]"

3. Let's do the example.

3.1. When we split the 'host' we land in 'IPv6reference' and then in
'IPv6address'.

3.2. In the 'hexpart' we land in the 3rd part with "::192" which is ok.

But what should happen now with '.9.5.5'?
It's definitly not a part of the description above but should be valid
as described in RFC 2732.

You should also change
"host          = hostname | IPv4address | IPv6reference"
to
"host          = hostname | IPv6reference | IPv4address"
because the IP4address is filled via the IPv6reference

IPv6 literals have been added to the list of possible identifiers
for the host portion of a server component, as described by RFC 2732,
but in the reverse order to reflect disambiguation rules.

Since RFC 2732 defers to RFC 2373 for definition of an IPv6 literal
address, which unfortunately has an incorrect ABNF description of
IPv6address, I created a new ABNF rule for IPv6address that matches
the text representations defined by Section 2.2 of RFC 2373.
Likewise, the definition of IPv4address has been improved in order to
limit each decimal octet to the range 0-255.

I think the consensus built in the IG and reported in 
draft-mealling-uri-ig-02.txt is a good place to start.
Especially the recommendation:

  1.  The W3C and IETF should jointly develop and endorse a model for
       URIs, URLs and URNs consistent with the '"Contemporary View"
       described in section 1, and which considers the additional URI
       issues listed or alluded to in section 3.

Just so you won't have to go dig the draft up, this is the "Contemporary
View":

   Over time, the importance of this additional level of hierarchy
   seemed to lessen; the view became that an individual scheme does not
   need to be cast into one of a discrete set of URI types such as
   "URL", "URN", "URC", etc.  Web-identifer schemes are in general URI
   schemes; a given URI scheme may define subspaces.  Thus "http:" is a
   URI scheme.  "urn:" is also a URI scheme; it defines subspaces,
   called "namespaces".  For example, the set of URNs of the form
   "urn:isbn:n-nn-nnnnnn-n" is a URN namespace.  ("isbn" is an URN
   namespace identifier.  It is not a "URN scheme" nor a "URI scheme").

   Further according to the contemporary view, the term "URL" does not
   refer to a formal partition of URI space; rather, URL is a useful but
   informal concept: a URL is a type of URI that identifies a resource
   via a representation of its primary access mechanism (e.g., its
   network "location"), rather than by some other attributes it may
   have.  Thus as we noted, "http:" is a URI scheme.  An http URI is a
   URL.  The phrase "URL scheme" is now used infrequently, usually to
   refer to some subclass of URI schemes which exclude URNs.

Fixed by rewriting the section on URI, URL, and URN, and changing
all use of the term URL in the specification to URI.

The only thing I want to include is the default: %xx means the character
encoded as xx in UTF-8.  That is already the default for MSIE and should
be for other browsers as well, and will simplify the specification.

I disagree. While it's the default in MSIE for URIs, the user enters
into the address bar, it's not the default for the vast majority of
%xx encoded octets requested by MSIE, they originate from HTML forms
where MSIE uses the document or user selected character encoding scheme
to generate the octets, hence most %xx encoded octets representing
non-ASCII characters are not part of valid UTF-8 sequences. There is no
facility to define any other encoding than UTF-8, hence applications
assuming UTF-8 encoding are said to fail.

I would be extremely delighted if we could just go and say
"it's UTF-8, and nothing else". Unfortunately, that's not
possible. But I think it's a very good idea to make clear
in the revision that UTF-8 is where things are moving,
rather than just the current

"For example, UTF-8 [UTF-8] defines a mapping from sequences
of octets to sequences of characters in the repertoire of ISO 10646."

While we are at it, what about changes due to Internationalized
Domain Names?
http://search.ietf.org/internet-drafts/draft-ietf-idn-uri-01.txt
proposes to lift the restriction that %hh cannot be used in the
host name part. [Currently, only %80 and higher are allowed,
but I plan to change that because it would really be silly to
keep it that way.]

Update the syntax of host names: Currently, this is one of the
only places where %hh-escaping isn't allowed. Implementations
are mixed, some browsers e.g. accept http://www.w%33.org while
others don't. So this may go under "(b) document variations in
current practice, as warnings to implementors." below.
With Internationalized Domain Names, allowing %hh in host names
is necessary for consistency.

The actual text is currently in
http://www.ietf.org/internet-drafts/draft-ietf-idn-uri-02.txt,
and there is some chance that the IDN WG moves this forward.
But in either way, it should be folded into the URI spec.

The example of resolving a relative URL could be improved.  It uses a
base of http://a/b/c/d;p?q

Not wanting to read the RFC end to end, it took me a bit of searching to
find that the ;p part is a "parameter" and the ?q part is a "query".
But I have no idea what their relevance is to this example.  It they are to be
ignored when attaching the relative parts, it would be nice to say so.

The basic expansion has one very confusing and not explained aspect.
The relative path g is said to expand to http://a/b/c/g instead of
http://a/b/c/d/g.  The other expansions are obvious once the "remove d"
rule is applied.  Would a base of http://a/b/c/d/ plus g expand to
http://a/b/c/d/g?

The examples should have enough annotation to
mostly stand on their own and to reinforce the concepts.

I found them to be very helpful in their current form. The
only thing I would state differently is the handling of
too many ../ in the resolved uri.

The RFC currently states that

base http://host/a/b
ref  ../../c
resolves to http://host/../c

and continues that removing the /.. at the beginning is allowed.

My observation is that removing /.. is the norm nowadays
and therefore the example should be the other way with a
note that keeping /.. is allowed.

The examples are intended to identify common bugs or deprecated features
in software.  The role of ";" changed from RFC 1808, so the tests can be
used to differentiate between an 1808-compliant parser and a 2396-compliant
parser, thus identifying places where changes are needed.

I'd like to expand the tests, particularly with other example base URI,
since there is one errata that would have been discovered that way.
More annotation is welcome.

http://lists.w3.org/Archives/Public/www-tag/2002Jul/0169.html

These look like interesting possible additions to the URI specification.

URI Resolution: 
  The process of determining an access mechanism and 
  appropriate parameters necessary to dereference a 
  URI. e.g. in the case of an HTTP URI, this process 
  resolves the URI into an IP address, a port number, 
  a host name (possibly optional) and a request URI.

  Resolution may require several iterations.

URI Dereference: 
  The process of using an access mechanism and 
  parameters generated by URI resolution to create, 
  inspect or modify resource state.

URI Retrieval: 
  The use of URI dereference to retrieve 
  representations of resource state. 

I note that Roy of late has been using URI as its own plural.
Elegant and defensible, but I prefer URIs as less surprising to the eye.
Even more, I prefer consistency.  Clearly this is a subject on which 
consensus is not remotely possible.

I prefer whichever one is easier to say while speaking, since I do not
believe in the theory that people expand acronyms as they read.

I am fine with either one, provided I only have to change it once.

Fixed by rewriting URI to "a URI" or URIs, as appropriate.

http://lists.w3.org/Archives/Public/uri/2002Sep/0016.html

At issue is the first sentence of the informal definition of resource in 
RFC 2396 1.1,

  A resource can be anything that has identity.

"that has identity" is redundant because *everything* has identity in 
the only reasonably straightforward understanding of identity, ie. the 
logical truth in all but the most obscure formal systems that,

  (Vx) x = x

Even though redundant, this qualifier has had the unfortunate 
consequence of leaving this sentence open to wildly different 
interpretations,

* It has been read as implying that the set of possible resources is a
  subset of the set of things: the subset that has identity as opposed
  to the subset that doesn't. Dan Brickley reports that this confusion,
  and the subsequent hunt for things which *don't* have identity and
  some means for identifying them, has caused trouble in RDF circles.

* It has been misread as,

    A resource can be anything that has an identifier (eg. a URI).

* It has been misread as,

    A resource can be anything that can be identified (via some
    effective mechanism).

I don't believe that any of these were the authors intent, so to clear 
up any confusion, the "that has identity" qualifier should be dropped.

That still leaves open the question of whether or not the residual,

  A resource can be anything.

is either true or makes sense. This is controversial, no doubt, but it's 
better not to have the controversy obscured by a distracting 
qualification.

The sentence says "can be", which implies exactly what I meant it to
imply: that anything with identity can be a resource but not necessarily
is a resource.  I see no reason to change it.  The important bit is that
sameness of identity is the important characteristic -- the defining
characteristic -- of a resource.

The goal of the sentence is to describe the essence of what it means
to be a resource.  None of the other suggestions do that.

Looking through the URI syntax in detail, I became aware
of the following 'anomaly': parameters are not allowed
in the first segment of a relative URI (if it doesn't start
with a slash). The relevant rules are:

 relativeURI   = ( net_path | abs_path | rel_path ) [ "?" query ]

 net_path      = "//" authority [ abs_path ]
 abs_path      = "/"  path_segments
 rel_path      = rel_segment [ abs_path ]

 rel_segment   = 1*( unreserved | escaped |
                     ";" | "@" | "&" | "=" | "+" | "$" | "," )

 path_segments = segment *( "/" segment )
 segment       = *pchar *( ";" param )
 param         = *pchar
 pchar         = unreserved | escaped |
                 ":" | "@" | "&" | "=" | "+" | "$" | ","

So in "abc;def/ghi;jkl", 'jkl' is a parameter, but 'def' isn't.
On the other hand, in "/abc;def/ghi;jkl", both 'def' and 'jkl'
are parameters.

Is this an error in the syntax, or can somebody explain this?

No, but I agree that it is confusing.  They are defined differently
because rel_segment cannot be empty.  Syntactically they are equivalent.
I'll find a better way to write it.

Fixed by removing the rule for param and simply stating why ";" and "="
are reserved within path segments.

It also looks like we'll have to switch to the formal ABNF of
RFC 2234 in order to define IPv4 addresses correctly.  At least
that will make the IESG happier, but it sure is a pain in the
editorial fingers.

The ad-hoc BNF syntax has been replaced with the ABNF of RFC 2234.
This change required all rule names that formerly included underscore
characters to be renamed with a dash instead.

Likewise, absoluteURI and relativeURI have been changed to absolute-URI
and relative-URI, respectively, for consistency.