Text/html

Text/html is the MIME Content Type for HTML marked-up text.

URLs:

RFC 1341 MIME (Multipurpose Internet Mail Extensions): Mechanisms for Specifying and Describing the Format of Internet Message Bodies

Detail:

Beyond the default text/plain, there are a number of MIME formats for representing extended text--text with embedded formatting and presentation information. Many such representations are to some degree readable without the software that interprets them--as with HTML documents. Other files, such as images and audio, contain unreadable data.

The MIME content type text/html can be defined further by specifying the HTML version, as with:"text/html; version=3.0."