HTML only tags the content of the file with certain attributes that are later defined by the browser used to view the file. HTML tags attribute type styles, insert graphics, sound, and video files in the text, and create hypertext links and forms. Hypertext is the most important capability of the HTML language. It means that any piece of text or graphic can link to another HTML document. The official HTML language is a specific set of tags that all browsers should interpret.
Some browsers are capable of interpreting additional tags outside the standard.
New tags are added to the standard set over time. It combined color graphics with HTML text capabilities for the first time. These days Netscape, developed by people formerly at NSCA, is becoming the browser of choice because of its speed and enhanced features. One internet access provider I know requires you to use the Web browser they developed.