As said earlier HTML is a standard and it keep undergoing new changes from w3consortion www.w3c.org to keep it up-to-date with new technologies and standard new version is introduce after some time, often years. For example XHTML is another newly introduce version of HTML,
(Although HTML5 currently is the latest version as of the time this written) and incorporates aspect of XML.
XHTML uses virtually all of the HTML elements. Nevertheless, XHTML imposes new rules that require you to squeeze your HTML tag to make your HTML webpage XHTML compliant. Let take a look at some of the rules:
XHTML encourage a lowercase. This means that the tags must be in lowercase. For example, <BODY> should be change to <body>
According to XHTML standard, every tag must be close, for example <title> is the opening tag, while </title> is the closing tag, and the text in-between the opening and the closing tag is content which the tag affects; even in a tag without content such as <br />, the tag is closed in the same tag that open it. Notice there is a space between the last letter of the tag and the forward slash.
Attributes must be enclosed with double quotations
<img src=”pix.jpg” />