W3C Markup Validation Service

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The Markup Validation Service is a validator of the World Wide Web Consortium (W3C), with the help of which Internet users can check documents in the description languages ​​HTML and XHTML for well-formed markup. Markup validation is an important step in ensuring the technical quality of websites; however, it is not a complete measure of compliance with web standards .


The Markup Validation Service began as a project by Gerald Oskoboiny under the name The Kinder, Gentler HTML Validator . It was developed as a more intuitive variant of the first online HTML validator, written by Dan Connolly and Mark Gaither and announced on July 13, 1994.

In September 1997 Oskoboiny started working for the W3C and on December 18, 1997 the W3C announced the W3C HTML Validator based on his work.

W3C also offers validation tools for various web technologies in addition to HTML / XHTML, for example for CSS , XML schema and MathML .

Supply of the browser

Many large web browsers are often tolerant of different types of errors and usually present a document without errors, even if it is not syntactically correct. Various other XML documents can also be validated with the Markup Validation Service, provided they have a reference to an internal or external DTD .

Criticism of the validator

All markup validators suffer from the inability to see the "big picture" of a web page. However, they often excel when it comes to finding missing closing tags and other formalities. This does not mean that the page is displayed in all browsers as intended by the creator.

DTD-based validators also have only a limited ability to evaluate attribute values ​​in terms of the specification documents. For example, when using the document type HTML 4.01 DOCTYPE, bgcolor = "fffff" is accepted as valid for the "body" element, although the value "fffff" lacks a preceding '#' character and has only 5 (instead of 6) hexadecimal digits contains. In addition, width = "really wide" is also considered valid for the "img" element. DTD-based validators are not technically capable of testing for these types of attribute value problems.

In addition, websites should be tested in as many browsers as possible to ensure that the validator's limitations are balanced and the website functions correctly.

CSS validation

While the HTML / XHTML validator of the W3C only evaluates pages that are written in such formats, another validator, such as the W3C CSS validator, is required to ensure that there are no errors in the associated cascading style sheet . CSS validators work in a similar way to HTML and XHTML validators, they apply current CSS standards to referenced CSS documents.

See also

Web links

Individual evidence

  1. a b About the W3C Markup Validation Service. Retrieved July 14, 2020 .
  2. ANNOUNCE: HaL Interactive HTML Validation Service , Dan Connolly, www-html -Mailingliste, July 13, 1994, accessed on July 10, 2012
  3. Gerald Oskoboiny: History of the Kinder, Gentler HTML Validator . March 22, 2003. Retrieved June 28, 2008.
  4. a b About the CSS Validator . World Wide Web Consortium. Retrieved June 24, 2012.
  5. ^ A b c Castro, Elisabeth: HTML, XHTML & CSS, Sixth Edition , pages 345–346. Visual Quickstart Guides, Peachpit Press, 2007. ISBN 0-321-43084-0