From Wikipedia, the free encyclopedia
Text after the # in a resource URIL
In computer
hypertext
, a
URI fragment
is a
string
of
characters
that refers to a
resource
that is subordinate to another, primary resource. The primary resource is identified by a
Uniform Resource Identifier
(URI), and the
fragment identifier
points to the subordinate resource.
The fragment identifier introduced by a
hash mark
#
is the optional last part of a
URL
for a document. It is typically used to identify a portion of that document. The generic syntax is specified in RFC 3986.
[1]
The hash mark separator in URIs is not part of the fragment identifier.
Basics
[
edit
]
In URIs, a hash mark
#
introduces the optional fragment near the end of the URL. The generic RFC 3986 syntax for URIs also allows an optional
query
part introduced by a question mark
?
. In URIs with a query and a fragment, the fragment follows the query. Query parts depend on the URI scheme and are evaluated by the server?e.g.,
http:
supports queries unlike
ftp:
. Fragments depend on the document
MIME type
and are evaluated by the client (
web browser
). Clients are not supposed to send URI fragments to servers when they retrieve a document.
[1]
[2]
A URI ending with
#
is permitted by the generic syntax and is a kind of empty fragment. In MIME document types such as
text/html
or any XML type, empty identifiers to match this syntactically legal construct are not permitted. Web browsers typically display the top of the document for an empty fragment.
The fragment identifier functions differently to the rest of the URI: its processing is exclusively
client-sided
with no participation from the
web server
, though the server typically helps to determine the MIME type, and the MIME type determines the processing of fragments. When an
agent
(such as a web browser)
requests
a
web resource
from a web server, the agent sends the URI to the server, but does not send the fragment. Instead, the agent waits for the server to send the resource, and then the agent processes the resource according to the document type and fragment value.
[3]
In an HTML web page, the agent will look for an anchor identified with an HTML tag that includes an
id=
or
name=
attribute equal to the fragment identifier.
Examples
[
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]
- In URIs for MIME
text/html
pages such as
http://www.example.org/foo.html#bar
the fragment refers to the element with
id="bar"
.
- Graphical Web browsers typically scroll to position pages so that the top of the element identified by the fragment id is aligned with the top of the viewport; thus fragment identifiers are often used in tables of content and in
permalinks
.
- The appearance of the identified element can be changed through the
:target
CSS
pseudoclass;
Wikipedia
uses this to highlight the selected reference. Notably CSS
display: block
can be used to show content only if it is the target, and otherwise hidden by
display: none
.
- The deprecated
name
attribute (allowed only for some elements) had a similar purpose in now obsolete browsers. If present
name
and
id
must be identical.
- In all
XML
document types including
XHTML
fragments corresponding to an
xml:id
or similar
id
attributes follow the
Name
-syntax and begin with a letter, underscore, or colon. Notably they cannot begin with a digit or hyphen.
[4]
xml:id
is one of the few generic XML attributes, e.g.,
xml:lang
, which can be used without explicitly declaring a namespace.
[5]
In XHTML
id
has to be used, because XHTML was specified before
xml:id
existed.
- In XML applications, fragment identifiers in a certain syntax can be
XPointers
; for example, the fragment identifier in the URI
http://www.example.org/foo.xml#xpointer(//Rube)
refers to all XML elements named "Rube" in the document identified by the URI http://www.example.org/foo.xml. An XPointer processor, given that URI, would obtain a representation of the document (such as by requesting it from the Internet) and would return a representation of the document's "Rube" elements.
- In
RDF
vocabularies, such as
RDFS
,
OWL
, or
SKOS
, fragment identifiers are used to identify resources in the same
XML Namespace
, but are not necessarily corresponding to a specific part of a document. For example,
http://www.w3.org/2004/02/skos/core#broader
identifies the concept "broader" in SKOS Core vocabulary, but it does not refer to a specific part of the resource identified by
http://www.w3.org/2004/02/skos/core
, a complete RDF file in which semantics of this specific concept is declared, along with other concepts in the same vocabulary.
- In URIs for MIME
text/plain
documents RFC 5147 specifies a fragment identifier for the character and line positions and ranges within the document using the keywords "
char
" and "
line
". Browser support seems lacking.
[6]
The following example identifies lines 11 through 20 of a text document:
http://example.com/document.txt#line=10,20
- In URIs for MIME
text/csv
documents, RFC 7111 specifies a fragment identifier as a selector for rows, columns, and cells using the keywords "
row
" , "
col
", and "
cell
", for example:
http://example.com/data.csv#row=4
? Selects the 4th row.
http://example.com/data.csv#col=2
? Selects 2nd column.
http://example.com/data.csv#row=5-7
? Selects three consecutive rows starting with 5th row.
http://example.com/data.csv#row=5-*
? Selects all rows starting with 5th row.
http://example.com/data.csv#cell=4,1-6,2
? Selects a region that starts at the 4th row and the 1st column and ends at the 6th row and the 2nd column.
- In URIs for MIME audio/*, image/*, video/* documents, very few have defined fragments or fragment semantics.
[7]
The Media Fragments URI 1.0 (basic) syntax supports addressing a media resource along two dimensions (temporal and spatial) using the keywords
t
and
xywh
. Therefore, one can use the following media fragments URI in the
src
attribute of the
audio
or
video
HTML5
element:
http://example.com/foo.mp4#t=10,20
http://example.com/bar.webm#t=40,80&xywh=160,120,320,240
- Other websites use the fragment part to pass some extra information to scripts running on them ? for example,
Google Video
understands permalinks in the format of
#01h25m30s
to start playing at the specified position,
[8]
and
YouTube
uses similar code such as
#t=3m25s
.
[9]
- In
JavaScript
, the fragment identifier of the current HTML or XHTML page can be accessed in the "hash" property
location.hash
? JavaScript can be also used with other document types. With the rise of
AJAX
, some websites use fragment identifiers to emulate the back button behavior of browsers for page changes that do not require a reload, or to emulate subpages.
- For example,
Gmail
uses a single URL for almost every interface ? mail boxes, individual mails, search results, settings ? the fragment is used to make these interfaces directly linkable.
[10]
- Adobe Flash
websites can use the fragment part to inform the user about the state of the website or web application, and to facilitate
deep linking
, commonly with the help of the SWFAddress JavaScript library.
- A URI that links to a
JSON
document can specify a pointer to a specific value.
[11]
- For example, a URL ending in
#/foo
could be used to extract the value from a key-value pair in a document beginning with
{ "foo": ["bar", "baz"], ... }
- In URIs for MIME
application/pdf
documents PDF viewers recognize a number of fragment identifiers.
[12]
[13]
For instance, a URL ending in
.pdf#page=35
will cause most readers to open the PDF and scroll to page 35. Several other parameters are possible, including
#nameddest=
(similar to HTML anchors),
#search="word1 word2"
,
#zoom=
, etc. Multiple parameters can be combined with ampersands:
http://example.org/doc.pdf#view=fitb&nameddest=Chapter3
.
- In
SVG
, fragments are allowed to specify arguments such as
viewBox()
,
preserveAspectRatio()
, and
transform()
.
[14]
Proposals
[
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]
Several proposals have been made for fragment identifiers for use with plain text documents (which cannot store anchor metadata), or to refer to locations within HTML documents in which the author has not used anchor tags:
- As of September 2012 the Media Fragments URI 1.0 (basic) is a
W3C
Recommendation.
[15]
- Chrome versions 80 and above
[16]
[17]
implement
W3C
's
WICG
Text Fragments,
[18]
so
#:~:text=foo
will cause the browser to search for
foo
, highlight the matching text, and scroll to it. Besides the start and end, the snippet can also specify a context: text that must precede or follow
foo
but will not be highlighted (
example that uses
#:~:text=night-,vision
to find 'vision' preceded by 'night'
).
- The
Python
Package Index appends the
MD5
hash of a file to the URL as a fragment identifier.
[19]
If MD5 were unbroken (it is a
broken hash function
), it could be used to ensure the
integrity
of the package.
https://pypi.python.org ... zodbbrowser-0.3.1.tar.gz#md5=38dc89f294b24691d3f0d893ed3c119c
- A
hash-bang
[20]
fragment is a fragment starting with an exclamation mark
!
. It was used in a now-deprecated approach to index dynamic
single-page applications
. An
exclamation mark
is illegal in
HTML4
, XHTML, and XML identifiers, granting certain degree of separation from that functionality. However, it is allowed in
HTML5
.
[21]
- Between 2009 and 2015,
Google Webmaster Central
proposed and then recommended an "AJAX crawling scheme"
[22]
[23]
using an initial exclamation mark in fragment identifiers for stateful
AJAX
pages:
http://example.com/page?query#!state
- Another implementation has been the replacement of
#!
with
?_escaped_fragment_=
[22]
- Hash-bang URIs have been considered problematic by a number of writers including Jeni Tennison at the W3C because they make pages inaccessible to those who do not have
JavaScript
activated in their browser. They also break
HTTP referer
headers as browsers are not allowed to send the fragment identifier in the Referer header.
[20]
- In 2015, Google deprecated their hash-bang AJAX crawling proposal, recommending instead the use of
progressive enhancement
and
HTML5
's
history.pushState()
[24]
method.
[25]
- Mozilla Foundation
employee Gervase Markham has proposed a fragment identifier for searching, of the form
#!s!search terms
. Adding a number after the s (
#!s10!
) indicates that the browser should search for the
n
th occurrence of the search term. A negative number (
#!s-3!
) starts searching backwards from the end of the document. A
Greasemonkey
script is available to add this functionality to compatible browsers.
[26]
http://example.com/index.html#!s3!search terms
- Erik Wilde and Marcel Baschnagel of the
ETH Zurich
extend this to also identify fragments in plain text documents using
regular expressions
, with the keyword "
match
".
[27]
They also describe a prototype implementation as an extension for the
Firefox
browser. For example, the following would find the case-insensitive text "RFC" anywhere in the document:
http://example.com/document.txt#match=[rR][fF][cC]
- K. Yee of the
Foresight Institute
proposes "extended fragment identifiers" delimited with
colons
and a keyword to differentiate them from anchor identifiers. A text search fragment identifier with "fragment specification scheme" id "
words
" is the first proposal in this scheme.
[28]
The following example would search a document for the first occurrence of the string "some context for a search term" and then highlight the words "search term":
http://example.com/index.html#:words:some-context-for-a-(search-term)
- The above scheme was implemented in Chrome version 80.
[29]
- The LiveURLs project
[30]
proposed a fragment identifier format for referring to a region of text within a page, of the form
#FWS+C
, where
F
is the length of the first word (up to five characters),
W
is the first word itself,
S
is the length of the selected text and
C
is a 32-bit
CRC
of the selected text.
[31]
They implemented a variant of this scheme as an extension for the Firefox browser,
[32]
using the form
#LFWS+C
, where
L
is the length of the fragment itself, in two
hex
digits. Linking to the word "Fragment" using the implemented variant would yield:
http://example.com/index.html#115Fragm8+-52f89c4c
- Up until Firefox 5, Firefox supported XPath links such as #xpath:/html/body/div[3] which could be used in conjunction with a bookmarklet such as
http://antimatter15.com/wp/2009/11/xpath-bookmark-bookmarklet/
to link within HTML documents that lacked proper IDs. This feature was removed as part of a code cleanup in
https://bugzilla.mozilla.org/show_bug.cgi?id=457102
- In
ePub
electronic book format, the EPUB Canonical Fragment Identifier (epubcfi,
[33]
2011-2017) defines a
W3C
/
IDPF
-standardized method for referencing arbitrary content using fragment identifiers to locate non-anchored text ranges via document structure and pattern matching. These dynamic deep links assist in locating content after text is updated and are used, for example, in
Apple Books
.
See also
[
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]
References
[
edit
]
- ^
a
b
"RFC 3986 Uniform Resource Identifier (URI): Generic Syntax"
. Internet Engineering Task Force. January 2005
. Retrieved
2012-03-06
.
- ^
R. Fielding, Ed., Adobe; J. Reschke, Ed., greenbytes (June 2014).
"Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing"
. Internet Engineering Task Force (IETF)
. Retrieved
2023-12-27
.
The target URI excludes the reference's fragment component, if any, since fragment identifiers are reserved for client-side processing
{{
cite web
}}
: CS1 maint: multiple names: authors list (
link
)
- ^
"Representation types and fragment identifier semantics"
.
Architecture of the World Wide Web, Volume One
.
W3C
. 2004
. Retrieved
2011-07-13
.
- ^
"Validity constraint: ID"
.
XML 1.0 (Fifth Edition)
.
W3C
. 2008
. Retrieved
2011-07-13
.
- ^
"xml:id Version 1.0"
.
W3C
. 2005
. Retrieved
2011-07-13
.
- ^
"Issue 77024"
.
Chromium
. 2011
. Retrieved
2011-07-13
.
- ^
"Media Type Review"
.
W3C Media Fragments Working Group
. 2009
. Retrieved
2009-04-29
.
- ^
"New Feature: Link within a Video"
. 2006-07-19
. Retrieved
2011-07-13
.
- ^
"Link To The Best Parts In Your Videos"
.
YouTube
. 2008-10-30
. Retrieved
2011-07-13
.
- ^
Link to Specific Content in Gmail
, Google Blogoscoped, 2007-11-17
- ^
Bryan, P (2013-04-02).
"RFC 6901 ? JavaScript Object Notation (JSON) Pointer"
. The Internet Society
. Retrieved
2022-07-14
.
- ^
"Parameters for Opening PDF Files ? Specifying parameters in a URL"
(PDF)
. Adobe. April 2007
. Retrieved
2017-09-20
.
- ^
Taft, E.; Pravetz, J.; Zilles, S.; Masinter, L. (May 2004).
"RFC 3778 ? The application/pdf Media Type"
.
tools.ietf.org
. The Internet Society.
doi
:
10.17487/RFC3778
. Retrieved
2017-09-20
.
- ^
"Linking ? SVG 1.1 (Second Edition)"
.
- ^
"Media Fragments URI 1.0 (basic) W3C Recommendation"
. Retrieved
2012-09-25
.
- ^
"Scroll to Text Fragment"
.
Chrome Platform Status
.
Google Chrome
. Retrieved
2020-05-18
.
- ^
Kelly, Gordon.
"Google Chrome 80 Released With Controversial Deep Linking Upgrade"
.
Forbes
. Retrieved
2020-06-04
.
- ^
"WICG/scroll-to-text-fragment: Proposal to allow specifying a text snippet in a URL fragment"
.
GitHub
.
WebPlatform.org
Incubator Community Group at
W3C
. Retrieved
2020-05-18
.
- ^
"Pypi md5 check support"
. Retrieved
2011-07-13
.
Pypi has the habit to append an md5 fragment to its egg urls, we'll use it to check the already present distribution files in the cache
- ^
a
b
"Hash URIs"
.
W3C Blog
. 2011-05-12
. Retrieved
2011-07-13
.
- ^
"HTML 5.1 2nd Edition"
.
W3C
. 2017
. Retrieved
2018-08-03
.
- ^
a
b
"Proposal for making AJAX crawlable"
. 2009-10-07
. Retrieved
2011-07-13
.
- ^
"(Specifications) Making AJAX Applications Crawlable"
. Google Inc
. Retrieved
2013-05-04
.
- ^
"Manipulating the browser history"
.
Mozilla Developer Network
. Retrieved
2017-02-23
.
- ^
"Deprecating our AJAX crawling scheme"
.
Official Google Webmaster Central Blog
. Retrieved
2017-02-23
.
- ^
Fragment Search
, gerv.net
- ^
Fragment identifiers for plain text files, Erik Wilde and Marcel Baschnagel, Swiss Federal Institute of Technology (ETH Zurich), Proceedings of the sixteenth ACM conference on Hypertext and hypermedia
doi
:
10.1145/1083356.1083398
- ^
Text-Search Fragment Identifiers
, K. Yee, Network Working Group, Foresight Institute, March 1998
- ^
bmcquade; bokan; nburris (2022-03-24).
"Feature: Scroll to Text Fragment"
.
Chrome Platform Status
. chromium.org
. Retrieved
2022-05-03
.
- ^
LiveURLs project
- ^
The technology behind LiveURLs
, accessed 2011-03-13
- ^
"Web Marker" Firefox add-on
, accessed 2011-03-13
- ^
"EPUB Canonical Fragment Identifiers 1.1"
.
idpf.org
. Retrieved
2020-06-03
.
External links
[
edit
]
- W3C
Media Fragments
Working Group, establishing a URI syntax and semantics to address media fragments in audiovisual material (such as a region in an image or a sub-clip of a video)
- MediaMixer
Community Portal
collects presentations, tutorials, use cases and demonstrators related to use of Media Fragment technology