<br> is for line breaking command

  HTML text is supposed to be written in the ISO Latin-1 character set. A complete overview of all the characters in this set is available from:
  o http://www.w3.org/pub/WWW/MarkUp/html3/latin1.html

 DHML used events, methods, properties to insulate dynamism in HTML Pages.
 Simple explanation :
  If anyone use JavaScript in a HTML page, called DHTML.

 XHTML Modularization is not aimed at the regular users of XHTML, but at designers of XHTML-based languages. It had been observed that companies and groups had the tendency to design their own versions of HTML and XHTML that were often not interoperable at basic levels. XHTML Modularization splits XHTML into a number of modules that can be individually selected when defining a new language; in this way any XHTML-based language that uses tables is guaranteed to use the same definition of tables, and not some divergent version. Modularization also makes it clear where it is OK to add new elements, and where it is not.

  HTML Tidy gives you the option to transform any HTML document into an XHTML one. Amaya is a browser/editor that will save HTML documents as XHTML.

  HTML is probably the most successful document markup language in the world. But when XML was introduced, a two-day workshop was organised to discuss whether a new version of HTML in XML was needed. The opinion at the workshop was a clear 'Yes': with an XML-based HTML other XML languages could include bits of XHTML, and XHTML documents could include bits of other markup languages. We could also take advantage of the redesign to clean up some of the more untidy parts of HTML, and add some new needed functionality, like better forms.

  It is, but in a different way to how previous versions of HTML were backwards compatible. Because earlier versions of HTML were special-purpose languages, it was necessary to ensure a level of backwards compatibility with new versions so that new documents would still be usable in older browsers. For instance, this is why the element has its content in an attribute rather than in the content of the element, since it would have shown up in older browsers.
However, thanks to XML and stylesheets, such strict element-wise backwards compatibility is no longer necessary, since an XML-based browser, of which at the time of writing means more than 95% of browsers in use, can process new markup languages without having to be updated. Much of XHTML 2 works already in existing browsers, browsers that are not pre-programmed to accept XHTML2. Much works, but not all: when forms and tables were added to HTML, people had to wait for new version of browsers; similarly some parts of XHTML 2, such as XForms and XML Events, still require user agents that understand that functionality.

  Although browsers are indeed important users of HTML and XHTML, there are other programs and systems that read those documents. Search engines for instance read documents, but are not browsers. By using the term "user agent" we are trying to remind people of the difference.
 For example, when you do a Google search often you will see under some of the search results something like "This web page uses frames, but your browser doesn't support them." therefore surely frightening off some people from clicking on that link. The author of the website in question hasn't realised that there are more than just browsers, and that they ought to include better text in their section, so that they don't appear so foolish when people search their site.