<hypertext, standard, web> (XHTML) A reformulation of HTML 4.01 in XML. Being XML means that XHTML can be viewed, edited, and validated with standard XML tools. At the same time, it operates as well as or better than HTML 4 in existing HTML 4 conforming user agents.
The most important change is that all elements must be terminated, either with a closing tag or using the <tag.../> shorthand. So, instead of
you would write
The space before the "/" is required by some older browsers. Other differences are that tag and attribute names should be lower case and all attributes should be quoted.