The HyperText Markup Language was invented by Tim Berners-Lee at CERN in the early 1990s as a way of sharing scientific documents. A major goal (in addition to hyper-linking) was to define the structure of a document in plain text separately from the formatting or presentation.
By the time HTML3 was well-established in the late 1990s there had been numerous additions and changes that ‘polluted’ the code with formatting options such as <font> tags and purely visual effects such as the <blink> and <marquee> tags.
HTML5 is the latest (and final) version that explicitly uses Cascading Style Sheets to change the appearance of the page content and also includes media tags such as <video>, <audio> and <canvas> that can display/play external content using the browser’s own capabilities.
| Version | HTML | HTML2 | HTML3 | HTML4 | HTML5 |
|---|---|---|---|---|---|
| Year introduced | 1991 | Nov 1995 | Jan 1997 | Dec 1997 | Oct 2014 |
| Comment | Only 18 tags including hyperlinks | Forms, tables, image-maps, internationalisation | First version specified by | W3C Standardised Document Object Model (DOM) | All modern |
Tags in HTML surround the content, giving it meaning within the document. For example there are 6 levels of heading tags ( <h1> to <h6> ) that show how important information is in a hierarchy. They are written using angle brackets. The closing tags also have a forward-slash before the name. There are a few ‘singleton tags’ that do not have a closing partner. These non-container tags include horizontal rulers <hr> , break tags <br> that leave a gap between sections and also image tags <img> that hold a reference to an externally-loaded picture. Tags can have attributes inside the opening tag in the form of key= “value” pairs… e.g. <hr size= “30” align= “center” > . Note that an <hr> tag should semantically separate different concepts… if you want to draw a horizontal line then do this with CSS style… <hr style= “height: 30; align: center;” >
The image file formats that are most commonly used on the web are: