W3C Markup Validation Service
Encyclopedia
The Markup Validation Service is a validator
by the World Wide Web Consortium
(W3C) that allows Internet
users to check HTML
and XHTML
documents for well-formed
markup. Markup validation is an important step towards ensuring the technical quality of web pages; however, is not a complete measure of Web standards
conformance.
In September 1997, Oskoboiny began working for the W3C, and on December 18, 1997, the W3C announced its W3C HTML Validator based upon his work.
Once the validator has read the page and determined the applicable standards it looks for such things as missing opening or closing tags, missing quotation marks and other hand-coding errors.
The validator then provides a report indicating that the coding is correct or not. Errors are noted in a list.
Sometimes, one error, such as neglecting to close a tag, can cause a cascade of errors through the page, producing dozens or even hundreds of noted errors. However when the page author addresses the first error listed it will also eliminate the "cascade errors".
are often tolerant of certain types of error, and may display a document successfully even if it is not syntactically correct. Certain other XML
documents can also be validated if they refer to an internal or external DTD
.
W3C also offers validation tools for web technologies other than HTML/XHTML, such as MathML
or CSS
.
DTD based validators are also limited in their ability to check attribute values according to many specification documents. For example, using an HTML 4.01 DOCTYPE, bgcolor="fffff" is accepted as valid for the "body" element even though the value "fffff" is missing a preceding '#' character and contains only 5 (instead of 6) hexadecimal digits. Also, for the "img" element, width="really wide" is also accepted as valid. DTD based validators are technically not able to test for these types of attribute value problems.
Furthermore, even if validated, all web pages should be tested in as many different browsers as possible to ensure that the limitations of the validator are compensated for and that the page works correctly.
Validator
A validator is a computer program used to check the validity or syntactical correctness of a fragment of code or document. The term is commonly used in the context of validating HTML, CSS and XML documents or RSS feeds though it can be used for any defined format or language.-HTML validator:In the...
by the World Wide Web Consortium
World Wide Web Consortium
The World Wide Web Consortium is the main international standards organization for the World Wide Web .Founded and headed by Tim Berners-Lee, the consortium is made up of member organizations which maintain full-time staff for the purpose of working together in the development of standards for the...
(W3C) that allows Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
users to check HTML
HTML
HyperText Markup Language is the predominant markup language for web pages. HTML elements are the basic building-blocks of webpages....
and XHTML
XHTML
XHTML is a family of XML markup languages that mirror or extend versions of the widely-used Hypertext Markup Language , the language in which web pages are written....
documents for well-formed
Well-formed element
In web page design, and generally for all markup languages such as SGML, HTML, and XML, a well-formed element is one that is either*opened and subsequently closed,*an empty element, which in that case must be terminated,...
markup. Markup validation is an important step towards ensuring the technical quality of web pages; however, is not a complete measure of Web standards
Web standards
Web standards is a general term for the formal standards and other technical specifications that define and describe aspects of the World Wide Web. In recent years, the term has been more frequently associated with the trend of endorsing a set of standardized best practices for building web sites,...
conformance.
History
The Markup Validation Service began as The Kinder, Gentler HTML Validator, a project by Gerald Oskoboiny. It was developed to be a more intuitive version of the first online HTML validator written by Dan Connolly and Mark Gaither, which was announced on July 13, 1994.In September 1997, Oskoboiny began working for the W3C, and on December 18, 1997, the W3C announced its W3C HTML Validator based upon his work.
Method of operation
HTML validators operate by comparing the mark-up on a web page to the W3C standards. The standards vary depending upon the declared version and so the validator will start by reading the DOCTYPE declaration to see which set of standards to apply.Once the validator has read the page and determined the applicable standards it looks for such things as missing opening or closing tags, missing quotation marks and other hand-coding errors.
The validator then provides a report indicating that the coding is correct or not. Errors are noted in a list.
Sometimes, one error, such as neglecting to close a tag, can cause a cascade of errors through the page, producing dozens or even hundreds of noted errors. However when the page author addresses the first error listed it will also eliminate the "cascade errors".
Browser accommodation
Many major browsersWeb browser
A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier and may be a web page, image, video, or other piece of content...
are often tolerant of certain types of error, and may display a document successfully even if it is not syntactically correct. Certain other XML
XML
Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....
documents can also be validated if they refer to an internal or external DTD
Document Type Definition
Document Type Definition is a set of markup declarations that define a document type for SGML-family markup languages...
.
W3C also offers validation tools for web technologies other than HTML/XHTML, such as MathML
MathML
Mathematical Markup Language is an application of XML for describing mathematical notations and capturing both its structure and content. It aims at integrating mathematical formulae into World Wide Web pages and other documents...
or CSS
Cascading Style Sheets
Cascading Style Sheets is a style sheet language used to describe the presentation semantics of a document written in a markup language...
.
Validator criticism
All mark-up validators suffer from an inability to see the "big picture" on a web page. However they excel at picking up missed closing tags and other technicalities. This does not mean that the page will display as the author intended in all browsers.DTD based validators are also limited in their ability to check attribute values according to many specification documents. For example, using an HTML 4.01 DOCTYPE, bgcolor="fffff" is accepted as valid for the "body" element even though the value "fffff" is missing a preceding '#' character and contains only 5 (instead of 6) hexadecimal digits. Also, for the "img" element, width="really wide" is also accepted as valid. DTD based validators are technically not able to test for these types of attribute value problems.
Furthermore, even if validated, all web pages should be tested in as many different browsers as possible to ensure that the limitations of the validator are compensated for and that the page works correctly.
CSS validation
While the W3C and other HTML and XHTML validators will assess pages coded in those formats, a separate validator is needed to confirm that there are no errors in the associated Cascading Style Sheet. CSS validators work in a similar manner to HTML and XHTML validators in that they apply current CSS standards to referenced CSS documents.See also
- CSE HTML ValidatorCSE HTML ValidatorCSE HTML Validator is a software program for Microsoft Windows 2000, Windows XP, Windows Server 2003, Windows Vista, Windows 7, and above that was created by Albert Wiersch and is developed and sold electronically by AI Internet Solutions based near Dallas, TX.CSE HTML Validator is designed to help...
, an offline HTMLHTMLHyperText Markup Language is the predominant markup language for web pages. HTML elements are the basic building-blocks of webpages....
and CSSCSS-Computing:*Cascading Style Sheets, a language used to describe the style of document presentations in web development*Central Structure Store in the PHIGS 3D API*Closed source software, software that is not distributed with source code...
validation program for Microsoft WindowsMicrosoft WindowsMicrosoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal... - HTML TidyHTML TidyHTML Tidy is a computer program and a library whose purpose is to fix invalid HTML and to improve the layout and indent style of the resulting markup....
, an offline markup validation program developed by Dave RaggettDave RaggettDave Raggett is a computer specialist who has played a major role in implementing the World Wide Web since 1992.He has been a W3C Fellow at the World Wide Web Consortium since 1995 and worked on many of the key web protocols, including HTTP, HTML, XHTML, MathML, XForms, and VoiceXML.Raggett wrote...
of W3C