All references are normative unless marked "Non-normative".

Augmented BNF for Syntax Specifications: ABNF (URL:, D. Crocker, P. Overell. IETF.
The 'about' URI scheme (URL:, S. Moonesamy. IETF.
(Non-normative) APNG Specification (URL: S. Parmenter, V. Vukicevic, A. Smith. Mozilla.
Accessible Rich Internet Applications (WAI-ARIA) (URL:, J. Craig, M. Cooper, L. Pappas, R. Schwerdtfeger, L. Seeman. W3C.
WAI-ARIA 1.0 User Agent Implementation Guide (URL:, J. Scheuhammer, M. Cooper, A. Snow-Weaver, M. Cooper. W3C.
(Non-normative) Authoring Tool Accessibility Guidelines (ATAG) 2.0 (URL:, J. Richards, J. Spellman, J. Treviranus. W3C.
(Non-normative) The Atom Syndication Format (URL:, M. Nottingham, R. Sayre. IETF.
Tags for Identifying Languages; Matching of Language Tags (URL:, A. Phillips, M. Davis. IETF.
(Non-normative) Behavioral Extensions to CSS (URL:, I. Hickson. W3C.
UAX #9: Unicode Bidirectional Algorithm (URL:, M. Davis, A. Lanin, A. Glass. Unicode Consortium.
(Non-normative) UTN #6: BOCU-1: MIME-Compatible Unicode Compression (URL:, M. Scherer, M. Davis. Unicode Consortium.
(Non-normative) UTR #26: Compatibility Encoding Scheme For UTF-16: 8-BIT (CESU-8) (URL:, R. McGowan. Unicode Consortium.
(Non-normative) Character Model for the World Wide Web 1.0: Fundamentals (URL:, M. Dürst, F. Yergeau, R. Ishida, M. Wolf, T. Texin. W3C.
Unicode Common Locale Data Repository (URL: Unicode.
(Non-normative) On computable numbers, with an application to the Entscheidungsproblem (URL:, A. Turing. In Proceedings of the London Mathematical Society, series 2, volume 42, pages 230-265. London Mathematical Society, 1937.
HTTP State Management Mechanism (URL:, A. Barth. IETF.
Cross-Origin Resource Sharing (URL:, A. van Kesteren. W3C.
(Non-normative) CP50220 (URL:, Y. Naruse. IANA.
(Non-normative) Content Security Policy (URL:, B. Sterne, A. Barth. W3C.
Cascading Style Sheets Level 2 Revision 1 (URL:, B. Bos, T. Çelik, I. Hickson, H. Lie. W3C.
(Non-normative) CSS Animations (URL:, D. Jackson, D. Hyatt, C. Marrin, S. Galineau, L. Baron. W3C.
CSS Styling Attribute Syntax (URL:, T. Çelik, E. Etemad. W3C.
CSS Color Module Level 3 (URL:, T. Çelik, C. Lilley, L. Baron. W3C.
(Non-normative) CSS Font Loading (URL:, T. Atkins. W3C.
(Non-normative) CSS Fonts (URL:, J. Daggett. W3C.
(Non-normative) CSS Generated Content (URL:, H. Lie, E. Etemad, I. Hickson. W3C.
(Non-normative) CSS Ruby Module Level 1 (URL:, E. Etemad, K. Ishii, R. Ishida. W3C.
(Non-normative) CSS Transitions (URL:, D. Jackson, D. Hyatt, C. Marrin, L. Baron. W3C.
(Non-normative) CSS Writing Modes (URL:, E. Etemad, K. Ishii. W3C.
(Non-normative) Custom Elements (URL:, D. Glazkov. W3C.
(Non-normative) Dynamic adaptive streaming over HTTP (DASH) (URL: ISO.
DOM (URL:, A. van Kesteren, A. Gregor, Ms2ger, A. Russell, R. Berjon. W3C.
DOM Parsing and Serialization (URL:, T. Leithead. Work in Progress. W3C.
(Non-normative) The DOT Language (URL: Graphviz.
ECMAScript Language Specification (URL: ECMA.
(Non-normative) HTML Editing APIs (URL:, A. Gregor. W3C Editing APIs CG.
Encoding (URL:, A. van Kesteren, J. Bell, A. Phillips. W3C.
Server-Sent Events (URL:, I. Hickson. W3C.
File API (URL:, A. Ranganathan. W3C.
(Non-normative) Fullscreen (URL:, A. van Kesteren, T. Çelik. W3C.
(Non-normative) Graphics Interchange Format (URL: CompuServe.
(Non-normative) Computer Graphics: Principles and Practice in C, Second Edition, J. Foley, A. van Dam, S. Feiner, J. Hughes. Addison-Wesley. ISBN 0-201-84840-6.
(Non-normative) Inter Gravissimas, A. Lilius, C. Clavius. Gregory XIII Papal Bull, February 1582.
(Non-normative) HTML to Platform Accessibility APIs Implementation Guide (URL: W3C.
(Non-normative) HTML5 differences from HTML4 (URL:, S. Pieters. W3C.
HTTP is the union of a set of RFCs:
Permanent Message Header Field Names (URL: IANA.
(Non-normative) Sourcing In-band Media Resource Tracks from Media Containers into HTML (URL:, S. Pfeiffer, B. Lund. W3C.
(Non-normative) ISO8601: Data elements and interchange formats — Information interchange — Representation of dates and times (URL: ISO.
(Non-normative) Requirements for Japanese Text Layout (URL: W3C.
JPEG File Interchange Format (URL:, E. Hamilton.
(Non-normative) The 'mailto' URI scheme (URL:, M. Dürst, L. Masinter, J. Zawinski. IETF.
Mathematical Markup Language (MathML) (URL:, D. Carlisle, P. Ion, R. Miner, N. Poppelier. W3C.
Media Fragments URI 1.0 (URL:, R. Troncy, E. Mannens, S. Pfeiffer, D. Van Deursen. W3C.
(Non-normative) Microformats Wiki: existing rel values (URL: Microformats.

As of today the Web community lacks a sufficiently complete, reliable, interoperable, and tested specification for the manner in which content sniffing takes place on the Web. We encourage implementers to exercise caution in this area as the Web community makes progress towards addressing this issue.

Media Type Sniffing (URL:, A. Barth, I. Hickson. IETF.

MNG (Multiple-image Network Graphics) Format (URL: G. Randers-Pehrson.
ISO/IEC 13818-1: Information technology — Generic coding of moving pictures and associated audio information: Systems. ISO/IEC.
ISO/IEC 14496-12: ISO base media file format. ISO/IEC.
Media Queries (URL:, H. Lie, T. Çelik, D. Glazman, A. van Kesteren. W3C.
(Non-normative) Gecko Plugin API Reference (URL: Mozilla.
SkeletonHeaders (URL: Xiph.Org.
Autodiscovery in HTML/XHTML (URL: In OpenSearch 1.1 Draft 4, Section 4.6.2.
The Web Origin Concept (URL:, A. Barth. IETF.
(Non-normative) Page Visibility (URL:, J. Mann, A. Jain. W3C.
(Non-normative) Document management — Portable document format — Part 1: PDF (URL: ISO.
Portable Network Graphics (PNG) Specification (URL:, D. Duce. W3C.
(Non-normative) Pointer Lock (URL:, V. Scheib. W3C.
(Non-normative) Polyglot Markup: HTML-Compatible XHTML Documents (URL:, E. Graff. W3C.
(Non-normative) The Properties and Promises of UTF-8 (URL:, M. Dürst. University of Zürich. In Proceedings of the 11th International Unicode Conference.
Public Suffix List (URL: Mozilla Foundation.
Progress Events (URL:, A. van Kesteren, C. McCathie Nevile; J. Song. W3C.
Domain Names - Concepts and Facilities (URL:, P. Mockapetris. IETF, November 1987.
Requirements for Internet Hosts -- Application and Support (URL:, R. Braden. IETF, October 1989.
(Non-normative) Character Mnemonics and Character Sets (URL:, K. Simonsen. IETF.
(Non-normative) Japanese Character Encoding for Internet Messages (URL:, J. Murai, M. Crispin, E. van der Poel. IETF.
(Non-normative) ISO-2022-JP-2: Multilingual Extension of ISO-2022-JP (URL:, M. Ohta, K. Handa. IETF.
(Non-normative) Korean Character Encoding for Internet Messages (URL:, U. Choi, K. Chon, H. Park. IETF.
(Non-normative) ASCII Printable Characters-Based Chinese Character Encoding for Internet Messages (URL:, Y. Wei, Y. Zhang, J. Li, J. Ding, Y. Jiang. IETF.
(Non-normative) Chinese Character Encoding for Internet Messages (URL:, HF. Zhu, DY. Hu, ZG. Wang, TC. Kao, WCH. Chang, M. Crispin. IETF.
Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types (URL:, N. Freed, N. Borenstein. IETF.
Key words for use in RFCs to Indicate Requirement Levels (URL:, S. Bradner. IETF.
(Non-normative) Japanese Character Encoding for Internet Messages (URL:, K. Tamaru. IETF.
The text/css Media Type (URL:, H. Lie, B. Bos, C. Lilley. IETF.
Returning Values from Forms: multipart/form-data (URL:, L. Masinter. IETF.
The "data" URL scheme (URL:, L. Masinter. IETF.
Algorithms and Identifiers for the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile (URL:, W. Polk, R. Housley, L. Bassham. IETF.
Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications (URL:, J. Jonsson, B. Kaliski. IETF.
The Text/Plain Format and DelSp Parameters (URL:, R. Gellens. IETF.
UTF-8, a transformation format of ISO 10646 (URL:, F. Yergeau. IETF.
Uniform Resource Identifier (URI): Generic Syntax (URL:, T. Berners-Lee, R. Fielding, L. Masinter. IETF.
Internationalized Resource Identifiers (IRIs) (URL:, M. Dürst, M. Suignard. IETF.
(Non-normative) Scripting Media Types (URL:, B. Höhrmann. IETF.
Guidelines and Registration Procedures for New URI Schemes (URL:, T. Hansen, T. Hardie, L. Masinter. IETF.
The Base16, Base32, and Base64 Data Encodings (URL:, S. Josefsson. IETF.
Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile (URL:, D. Cooper, S. Santesson, S. Farrell, S. Boeyen, R. Housley, W. Polk. IETF.
Internet Message Format (URL:, P. Resnick. IETF.
(Non-normative) URI Scheme for Global System for Mobile Communications (GSM) Short Message Service (SMS) (URL:, E. Wilde, A. Vaha-Sipila. IETF.
Internationalizing Domain Names in Applications (IDNA) (URL:, P. Faltstrom, P. Hoffman, A. Costello. IETF.
Use of the Content-Disposition Header Field in the Hypertext Transfer Protocol (HTTP) (URL:, J. Reschke. IETF.
(Non-normative) vCard Format Specification (URL:, S. Perreault. IETF.
The 'Codecs' and 'Profiles' Parameters for "Bucket" Media Types (URL:, R. Gellens, D. Singer, P. Frojdh. IETF.
XML Media Types (URL:, H. Thompson, C. Lilley. IETF.
(Non-normative) Use Cases & Exploratory Approaches for Ruby Markup (URL:, R. Ishida. W3C.
(Non-normative) UTR #6: A Standard Compression Scheme For Unicode (URL:, M. Wolf, K. Whistler, C. Wicksteed, M. Davis, A. Freytag, M. Scherer. Unicode Consortium.
Selectors (URL:, E. Etemad, T. Atkins. W3C.
IEC 61966-2-1: Multimedia systems and equipment — Colour measurement and management — Part 2-1: Colour management — Default RGB colour space — sRGB (URL:!OpenDocument&Click=). IEC.
Scalable Vector Graphics (SVG) 1.1 (Second Edition) (URL:, E. Dahlström et al. W3C.
(Non-normative) Tor (URL:
(Non-normative) Working with Time Zones (URL:, A. Phillips, N. Lindenberg, M. Davis, M.J. Dürst, F. Sasaki, R. Ishida. W3C.
Typed Array Specification (URL:, D. Herman, K. Russell. Khronos.
(Non-normative) Time Zone Database (URL: IANA.
(Non-normative) User Agent Accessibility Guidelines (UAAG) 2.0 (URL:, J. Allan, K. Ford, J. Richards, J. Spellman. W3C.
(Non-normative) UndoManager and DOM Transaction (URL:, R. Niwa.
The Unicode Standard (URL: Unicode Consortium.
(Non-normative) A composite approach to language/encoding detection (URL:, S. Li, K. Momoi. Netscape. In Proceedings of the 19th International Unicode Conference.

Note: URLs can be used in numerous different manners, in many differing contexts. For the purpose of producing strict URLs one may wish to consider [RFC3986] [RFC3987]. The W3C URL specification defines the term URL, various algorithms for dealing with URLs, and an API for constructing, parsing, and resolving URLs. Developers of Web browsers are advised to keep abreast of the latest URL developments by tracking the progress of We expect that the W3C URL draft will evolve along the Recommendation track as the community converges on a definition of URL processing.

Most of the URL-related terms used in the HTML specification (URL, absolute URL, relative URL, relative schemes, scheme component, scheme data, username, password, host, port, path, query, fragment, percent encode, get the base, and UTF-8 percent encode) can be straightforwardly mapped to the terminology of [RFC3986] [RFC3987]. The URLUtils (formerly known as URL) collection of attributes (e.g. href and protocol) and its required definitions (input, query encoding, url, update steps, set the input) are considered common practice nowadays. Some of the URL-related terms are still being refined (e.g. URL parser, parse errors, URL serializer, default encode set, and percent decode).

As a word of caution, there are notable differences in the manner in which Web browsers and other software stacks outside the HTML context handle URLs. While no changes would be accepted to URL processing that would break existing Web content, some important parts of URL processing should therefore be considered as implementation-defined (e.g. parsing file: URLs or operating on URLs that would be syntax errors under the [RFC3986] [RFC3987] syntax).

URL (URL:, E. Arvidsson, M.[tm] Smith. W3C.

(Non-normative) UTF-7: A Mail-Safe Transformation Format of Unicode (URL:, D. Goldsmith, M. Davis. IETF.
(Non-normative) Multilingual form encoding (URL:, M. Dürst. W3C.
(Non-normative) UTR #36: Unicode Security Considerations (URL:, M. Davis, M. Suignard. Unicode Consortium.
(Non-normative) Web Content Accessibility Guidelines (WCAG) 2.0 (URL:, B. Caldwell, M. Cooper, L. Reid, G. Vanderheiden. W3C.
(Non-normative) WebGL Specification (URL:, D. Jackson. Khronos Group.
Web IDL (URL:, C. McCormack. W3C.
(Non-normative) Web Linking (URL:, M. Nottingham. IETF.
Web Messaging (URL:, I. Hickson. W3C.
WebM Container Guidelines (URL: The WebM Project.
Web Storage (URL:, I. Hickson. W3C.
(Non-normative) WebVTT (URL:, S. Pfeiffer, P. Jägenstedt, I. Hickson (previous editor). W3C.
(Non-normative) Web Workers (URL:, I. Hickson. W3C.
(Non-normative) The WHATWG Wiki (URL: WHATWG.
The WebSocket protocol (URL:, I. Fette, A. Melnikov. IETF.
Recommendation X.690 — Information Technology — ASN.1 Encoding Rules — Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER), and Distinguished Encoding Rules (DER) (URL: International Telecommunication Union.
(Non-normative) XMLHttpRequest Level 1 (URL:, A. van Kesteren, J. Aubourg, J. Song, H.R.M. Steen. W3C.
Extensible Markup Language (URL:, T. Bray, J. Paoli, C. Sperberg-McQueen, E. Maler, F. Yergeau. W3C.
XML Base (URL:, J. Marsh, R. Tobin. W3C.
Namespaces in XML (URL:, T. Bray, D. Hollander, A. Layman, R. Tobin. W3C.
XML Path Language (XPath) Version 1.0 (URL:, J. Clark, S. DeRose. W3C.
(Non-normative) XSL Transformations (XSLT) Version 1.0 (URL:, J. Clark. W3C.