SGML (of which HTML is an application) has always been a way to serialize trees. XML made it clearer (by simplifying the syntax), but it's nothing new.

Most templating systems do treat HTML as text, but not all of them. I use AxKit, a web framework based on XML and XSLT

XSLT is a language specifically designed for tree manipulations. Not exactly every tree manipulation: it is more oriented towards down-translations (from structure to presentation), but it is Turing-complete, and I've used it successfully in a number of occasions.

It is not compact, it is not "quick & dirty", but I find it to be the easiest way (for me) to manipulate XML data.

You can use XML::LibXML to parse HTML documents, and XML::LibXSLT to transform them.

And (referring to a previous post) some Web graphics/designers are starting to learn XSLT, since they can use it independently from the language used by the developer.

-- 
        dakkar - Mobilis in mobile