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<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>The <a
href="http://www.w3.org/TR/REC-html40/references.html">URI reference</a> in the
HTML 4 refers to <a href="http://www.ietf.org/rfc/rfc2396.txt">RFC 2396</a> which
is obsolete by <a href="http://www.ietf.org/rfc/rfc3986.txt">RFC 3986</a>.
The latter document has a new section 2.5: "Identifying Data",
containing the following new material:<o:p></o:p></span></font></p>
<p class=MsoBlockText><font size=3 face="Times New Roman"><span lang=EN-US
style='font-size:12.0pt'>URI characters provide identifying data for each of
the URI components, serving as an external interface for identification between
systems. Although the presence and nature of the URI production interface
is hidden from clients that use its URIs (and is thus beyond the scope of the
interoperability requirements defined by this specification), it is a frequent
source of confusion and errors in the interpretation of URI character
issues. Implementers have to be aware that there are multiple character
encodings involved in the production and transmission of URIs: local name and
data encoding, public interface encoding, URI character encoding, data format encoding,
and protocol encoding.</span></font><font size=2 face=Arial><span lang=EN-US
style='font-size:10.0pt;font-family:Arial'><o:p></o:p></span></font></p>
<p class=MsoBlockText><b><font size=3 face="Times New Roman"><span lang=EN-US
style='font-size:12.0pt;font-weight:bold'>Local names, such as file system
names, are stored with a local character encoding</span></font></b><span
lang=EN-US>. URI producing applications (e.g., origin servers) will
typically use the local encoding as the basis for producing meaningful
names. The URI producer will transform the local encoding to one that is
suitable for a public interface and then transform the public interface
encoding into the restricted set of URI characters (reserved, unreserved, and
percent-encodings). Those characters are, in turn, encoded as octets to be used
as a reference within a data format (e.g., a document charset), and such data
formats are often subsequently encoded for transmission over Internet
protocols.<o:p></o:p></span></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>The new statements above are slightly incompatible
with what <a href="http://www.w3.org/TR/REC-html40/appendix/notes.html#h-B.2.1">HTML
URI encoding specification</a> says: <o:p></o:p></span></font></p>
<p class=MsoBlockText><font size=3 face="Times New Roman"><span lang=EN-US
style='font-size:12.0pt'>URIs do not contain non-ASCII values <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>That statement is true for what the RFC calls
"public interface encoding": it seems reasonable that the user agent
should use an URL when it requests an external resource; however, requiring
that HTML documents should use a public URI for resources that the user agent
is expected to serve without communicating with an external server, such as
local files identified using then file scheme, seems an excessive complication
to me. Internet Explorer <a href="http://blogs.msdn.com/ie/atom.xml">does
not respect</a> this prohibition because it uses IRIs, not URIs, internally,
and converts them to URLs if needed when it communicates with an external
server. If an external URL is specified in the source document as
percent-encoded, it is passed without altering because encoding is not needed
and the server is responsible for decoding; however, there is no server to
decode a local URL and it remains unresolved. That is not compliant with
the current standard, but I think in this case the implementation is right and
the standard needs some freedom with respect to local URLs.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>Of course, one could always do away with an argument
that an HTML document containing reference to a local resource cannot be
published and can be authored as noncompliant. However, this is only
partially true. The reason is that the prohibition of B.2.1 propagated to
the XSLT specification that refers to it explicitly where it specifies how URI
attributes should be transformed in <a
href="http://www.w3.org/TR/xslt#section-HTML-Output-Method">html mode</a>.
In effect, a document produced by a conforming XSLT processor for local usage
is perfectly valid and perfectly useless: hyperlinks are broken and images do
not show up.<o:p></o:p></span></font></p>
<p class=MsoListBullet><![if !supportLists]><font size=3 face=Symbol><span
lang=EN-US style='font-size:12.0pt;font-family:Symbol'><span style='mso-list:
Ignore'>·<font size=1 face="Times New Roman"><span style='font:7.0pt "Times New Roman"'>
</span></font></span></span></font><![endif]><span lang=EN-US>My suggestion: The
constraints for URLs denoting local resources should be relaxed.<o:p></o:p></span></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>I understand that this is fixed by <a
href="http://www.whatwg.org/specs/web-apps/current-work/multipage/section-document.html">HTML
5</a>, so this is perhaps the good news:<o:p></o:p></span></font></p>
<p class=MsoBlockText><font size=3 face="Times New Roman"><span lang=EN-US
style='font-size:12.0pt'>The </span></font><code><b><font size=2 color=black
face="Courier New"><span lang=EN-US style='font-size:10.0pt;color:black;
font-weight:bold'>href</span></font></b></code><span lang=EN-US> content
attribute, if specified, must contain a URI (or IRI).</span><font size=2><span
lang=EN-US style='font-size:10.0pt'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>Best regards,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>Christopher Yeleighton<o:p></o:p></span></font></p>
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