Do I have to know HTML or SGML before I learn XML?

<script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"> </script> No, although it's useful because a lot of XML terminology and practice derives from 15 years' experience of SGML. Be aware that `knowing HTML' is not the same as `understanding SGML' . Although HTML was written as an SGML application, browsers ignore most of it (which is why so many useful things don't work), so just because something is done a certain way in HTML browsers does not mean it's correct, least of all in XML.