![['Neverending story' by Alexandre Duret-Lutz. A framed photo of books with the droste effect applied. Licensed under creative commons.]](http://farm1.static.flickr.com/90/252757784_3de44cbeb4_m_d.jpg)
Information about URI Fragments, the portion of URIs
that follow the '#' at the end and that are used to navigate within a document, is scattered throughout various documents which I usually have to hunt down. Instead I'll link to them all here.
Definitions. Fragments are defined in the URI RFC which states that they're used to identify a secondary resource that is related to the primary resource identified by the URI as a subset of the primary, a view of the primary, or some other resource described by the primary. The interpretation of a fragment is based on the mime type of the primary resource. Tim Berners-Lee notes that determining fragment meaning from mime type is a problem because a single URI may contain a single fragment, however over HTTP a single URI can result in the same logical resource represented in different mime types. So there's one fragment but multiple mime types and so multiple interpretations of the one fragment. The URI RFC says that if an author has a single resource available in multiple mime types then the author must ensure that the various representations of a single resource must all resolve fragments to the same logical secondary resource. Depending on which mime types you're dealing with this is either not easy or not possible.
HTTP. In HTTP when URIs are used, the fragment is not included. The General Syntax section of the HTTP standard says it uses the definitions of 'URI-reference' (which includes the fragment), 'absoluteURI', and 'relativeURI' (which don't include the fragment) from the URI RFC. However, the 'URI-reference' term doesn't actually appear in the BNF for the protocol. Accordingly the headers like 'Request-URI', 'Content-Location', 'Location', and 'Referer' which include URIs are defined with 'absoluteURI' or 'relativeURI' and don't include the fragment. This is in keeping with the original fragment definition which says that the fragment is used as a view of the original resource and consequently only needed for resolution on the client. Additionally, the URI RFC explicitly notes that not including the fragment is a privacy feature such that page authors won't be able to stop clients from viewing whatever fragments the client chooses. This seems like an odd claim given that if the author wanted to selectively restrict access to portions of documents there are other options for them like breaking out the parts of a single resource to which the author wishes to restrict access into separate resources.
HTML. In HTML, the HTML mime type RFC defines HTML's fragment use which consists of fragments referring to elements with a corresponding 'id' attribute or one of a particular set of elements with a corresponding 'name' attribute. The HTML spec discusses fragment use additionally noting that the names and ids must be unique in the document and that they must consist of only US-ASCII characters. The ID and NAME attributes are further restricted in section 6 to only consist of alphanumerics, the hyphen, period, colon, and underscore. This is a subset of the characters allowed in the URI fragment so no encoding is discussed since technically its not needed. However, practically speaking, browsers like FireFox and Internet Explorer allow for names and ids containing characters outside of the defined set including characters that must be percent-encoded to appear in a URI fragment. The interpretation of percent-encoded characters in fragments for HTML documents is not consistent across browsers (or in some cases within the same browser) especially for the percent-encoded percent.
Text. Text/plain recently got a fragment definition that allows fragments to refer to particular lines or characters within a text document. The scheme no longer includes regular expressions, which disappointed me at first, but in retrospect is probably good idea for increasing the adoption of this fragment scheme and for avoiding the potential for ubiquitous DoS via regex. One of the authors also notes this on his blog. I look forward to the day when this scheme is widely implemented.
XML. XML has the XPointer framework to define its fragment structure as noted by the XML mime type definition. XPointer consists of a general scheme that contains subschemes that identify a subset of an XML document. Its too bad such a thing wasn't adopted for URI fragments in general to solve the problem of a single resource with multiple mime type representations. I wrote more about XPointer when I worked on hacking XPointer into IE.
SVG and MPEG. Through the Media Fragments Working Group I found a couple more fragment scheme definitions. SVG's fragment scheme is defined in the SVG documentation and looks similar to XML's. MPEG has one defined but I could only find it as an ISO document "Text of ISO/IEC FCD 21000-17 MPEG-12 FID" and not as an RFC which is a little disturbing.
AJAX. AJAX websites have used fragments as an escape hatch for two issues that I've seen. The first is getting a unique URL for versions of a page that are produced on the client by script. The fragment may be changed by script without forcing the page to reload. This goes outside the rules of the standards by using HTML fragments in a fashion not called out by the HTML spec. but it does seem to be inline with the spirit of the fragment in that it is a subview of the original resource and interpretted client side. The other hack-ier use of the fragment in AJAX is for cross domain communication. The basic idea is that different frames or windows may not communicate in normal fashions if they have different domains but they can view each other's URLs and accordingly can change their own fragments in order to send a message out to those who know where to look. IMO this is not inline with the spirit of the fragment but is rather a cool hack.
![[Many books in large bookcase. Photo creator http://flickr.com/people/babblingdweeb/]](http://farm1.static.flickr.com/18/23816128_d4acb70b2d_m_d.jpg)
I use my recently added
books feed from LibraryThing, a site I've mentioned before where you track, review, recommend, and share your books, and I put the recently added
books on my page. I thought it might be nice to include the book covers so I suggested adding book covers to RSS feeds in
LibraryThings 'Recommend Site Improvements' group. The next day I had a response from the founder and lead developer Tim Spalding who
had started implementing the feature. I noticed a few bugs, reported them on the same thread, and he fixed them soon after. Fantastic! It makes me want to upgrade to a paying account.
Incidentally, if you notice the Ghost in the Shell book appear multiple times in my RSS feed its due to the previously mentioned iterative bug fixes. The same item appeared multiple times slightly differently with each bug fix and your RSS aggregator may have picked them up as distinct items.
IPv6 address syntax consists of 8 groupings of colon delimited 16-bit hex values making up the 128-bit address. An optional double colon
can replace any consecutive sequence of 0 valued hex values. For example the following is a valid IPv6 address: fe80::2c02:db79
Some IPv6 addresses aren't global and in those cases need a scope ID to describe their context. These get a '%' followed by the scope ID.
For example the previous example with a scope ID of '8' would be: fe80::2c02:db79%8
IPv6 addresses in URIs may appear in the host section of a URI as long as they're enclosed by square brackets. For example:
http://[fe80::2c02:db79]/. The RFC explicitly notes that there isn't a way to add a scope ID to the IPv6 address in a URI. However a draft document describes adding
scope IDs to IPv6 addresses in URIs. The draft document uses the IPvFuture production from the URI RFC with a 'v1' to add a new
hostname syntax and a '+' instead of a '%' for delimiting the scope id. For example: http://[v1.fe80::2c02:db79+8]/. However, this is still a draft document, not a final
standard, and I don't know of any system that works this way.
In Windows XPSP2 the IPv6 stack is available but disabled by default. To enable the IPv6 stack, at a command prompt run 'netsh interface ipv6 install'. In Vista IPv6 is the on by default and cannot be turned off, while the IPv4 stack is optional and may be turned off by a command similar to the previous.
Once you have IPv6 on in your OS you can turn on IPv6 for IIS6 or just use IIS7. The address ::1 refers to the local machine.
In some places in Windows like UNC paths, IPv6 addresses aren't allowed. In those cases you can use a Vista DNS IPv6 hack that lives in the OS
name resolution stack that transforms particularly crafted names into IPv6 addresses. Take your IPv6 address, replace the ':'s with '-'s and the '%' with an 's' and then append '.ipv6-literal.net'
to the end. For example: fe80--2c02-db79s8.ipv6-literal.net. That name will resolve to the same example I've been using in Vista. This transformation occurs inside the system's local
name resolution stack so no DNS servers are involved, although Microsoft does own the ipv6-literal.net domain name.
MSDN describes IPv6 addresses in URIs in Windows and I've described IPv6 addresses in URIs in IE7. File URIs in
IE7 don't support IPv6 addresses. If you want to put a scope ID in a URI in IE7 you use a '%25' to delimit the scope ID and due to a bug you must have at least two digits in your scope ID. So,
to take the previous example: http://[fe80::2c02:db79%2508]/. Note that its 08 rather than just 8.
Two and half weeks ago Sarah and I went to Las Vegas where I got to
see Jesse, Pat, Chris, and (briefly because he's some kind of big shot too busy for his friends now etc) Grib from college. They're mostly in San Jose and I hadn't seen them for a while so it was a
lot of fun to hang out. We all stayed at the MGM which is a nice hotel with some good restaurants. In other Vegas related links, Sarah added Sarah's Las Vegas restaurant reviews to her reviews and Jesse has Jesse's Vegas
photos up too.
Sarah and I saw the Blue Man Group (video from a concert) and the Price is Right Live Show. The Blue Man Group
was very cool although the music was all rock with a heavy drum focus (not depicted in the videos I linked) which I got a little tired of. But despite that I really enjoyed the show, very funny and
I totally recommend it. The Price is Right Live Show is like the regular show on TV except the recording is not televised and its not hosted by Bob Barker or Drew Carey. So folks from the audience
are still called up to play the same games and really win prizes. It was advertised as hosted by Todd Newton, B-list game show host, but was instead
hosted by JD Roberto who hosted such things as "Reality Remix" and the show "Are You Hot? The Search for America's Sexiest People". The showcase
showdown included the 2008 version of my car and thankfully I wasn't picked to compete for that because, well I don't know where they bought the car, but I would have gotten the price very wrong.
We sat right next to the stage for that show and had a good time.
For New Years Eve Sarah and I stayed in and watched the glitched Seattle Space Needle fireworks show from a safe distance. On New Years we went to a pot-luck at Todd's house and had a fun time. Todd's place
is on the top of a hill and has a lovely view of Washington's snow-capped mountains.
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