Validated HTML Markup

HyperText Markup Language (HTML) is used to create web pages. When HTML Markup has been checked for compliance against a published standard and doesn’t contain any errors it is known as Valid HTML. The World Wide Web Consortium (W3C) publishes the recommendations for the latest HTML specifications.

A web designer can use an online checking service to validate the markup and see whether it follows the relevant standards. If any errors are detected the web page can be corrected.

HTML Standards

  • HTML was devised by Tim Berners-Lee in 1989 and was first published as a standard by the Internet Engineering Task Force (IETF) in June 1993.
  • HTML 2.0 was published in November 1995.
  • HTML 3.2 was published in January 1997.
  • HTML 4.0 was published in December 1997. There are three versions:
    - Strict, in which deprecated elements are forbidden
    - Transitional, in which deprecated elements are allowed
    - Frameset, in which mostly only frame related elements are allowed
  • HTML 4.01 was published in December 1999. The Strict, Transitional or Frameset versions are still included.
  • ISO HTML (ISO/IEC 15445:2000) was published in May 2000 as an ISO/IEC international standard. It is based on HTML 4.01 Strict.
  • HTML 5.0 was published in October 2014.
  • HTML 5.1 was published in November 2016.
  • HTML 5.2 was published in December 2017.


XHTML (eXtensible HyperText Markup Language) is a specification that was developed to reproduce, simplify and extend HTML 4.01 based on the XML format.

  • XHTML 1.0 was published in January 2000 and revised in August 2002. Strict, Transitional or Frameset versions are included.
  • XHTML 1.1 was published in May 2001. It is based on XHTML 1.0 Strict.
  • XHTML 2.0 was under development until 2009. The emergence of HTML 5 prompted a change in strategy.
  • XHTML 5 is the XML serialisation of HTML5.
  • XHTML+RDFa is an extended version of XHTML that supports RDF.

Why Valid HTML is important

All that a web browser can do is read the code from a web page and display the results. If it finds an error in the code it will try to correct the problem and carry on. So the first stage in HTML Validation is to locate and correct errors to minimise problems caused by incorrect code.

However there are many types of web browsers to choose from and web site visitors can choose the type of web browser they want to use in the same way that they can choose between different makes of car. At any one time there are old versions being used, new ones, fast ones, slow ones and some imperfect but widely used ones. The web designer has to cater for them all and would ideally like to create a consistent look but accepts that different web browsers can display the same web page very differently.

HTML standards have been created with backwards compatibility in mind so if the web page is written in valid HTML and viewed in an older web browser the worst case scenario should be a few graceful errors.

A web designer could create multiple versions of the same web page for different web browsers or try to resolve the incompatibilities by using complicated workarounds. However, most of the major web browser developers are working towards full support of the latest standards, so in time more and more people will use a standards compliant browser and will see the web site closer to the way the designer intended.

Working to the latest standards doesn’t guarantee that a web site will be problem free but an experienced designer can work around many of the design limitations and cater for the widest possible audience. Creating web pages using valid HTML will also ensure that search engines can understand the content of a web page correctly which will help to improve search engine optimisation and the position of the site in search engine results pages.