In 1993 HTML was invented in order to ease the way of publishing information on Internet. The standard language was for years used by universities to share and publish documentation on internet between the institutions all over the world.
Today most experienced web developers are familiar with the XHTML language for web publishing and standardised. The standard has been more and more implemented in newer website production but is still very rarely used as much as it should.
Standars for website publishing has been more and more understood and integrated with new technologies such as PHP, Ajax, JavaScript and DHTML. The importance to use the standard has also to do with the possibility of Search engine optimization and content devided from the website layout. In best practice XHTML 1.0 strict should be used for best crossbrowser and technical implementation to all platforms.