Templating frameworks which morph into crappy languages

This happens often in the computer industry where people are trying to separate out say XML and how the data in a source is formatted.

The templating starts off simple and then morphs into a terrible language with awful half thought out syntax.

An example of that would be XSLT. Never heard of XSLT? Well that is because it was awful! It a language for processing XML that was itself defined in XML. It had an obtuse syntax and it was really slow.