[cess11]

Once upon a time HTML was a kind of XML, which is why the current version is very similar to XML and hence painful to write. This in turn is why we tend to use programmatic tools to handle the HTML, and you should if you work with XML too.

[samus]

HTML5 is unlike XML in very important regards, which makes it actually quite difficult for tools to handle. But easier than XML. XHTML was quite annoying to write as far as I remember.

[MattPalmer1086]

In fact, HTML predates XML. Both can be seen as types of SGML.