History

• Web pages have been mainly constructed using HTML (HyperText Markup Language). This is the text used to design a website and to tell a computer what to do and how the page should be viewed. Design advancements have allowed for the creation of XHTML (Extensible HyperText Markup Language), which has aided in streamlining websites and making them universally compatible over different browsers.
  
  

Use

• XHTML is a subset of XML (Extensible Markup Language). XML can be used to structure many kinds of information, with its XHTML subset focusing on website design. XHTML is very similar to HTML in appearance on both the programming side as well its final output as a Web page.
  
  

Association

• The .xht file extension is a text file associated with the XHTML programming language. This type of file may be seen when creating or editing a website.