Lots of Zimlets can be built from just the .xml file. To be honest most do one or more things that you must write in
JS code. So if your doing some custom popup or want special UI interactions you'll want to have a .
js file loaded with your Zimlet to host that code. Can you give us some more detail or an example of the text you want to match on and exactly what the user would do.. (ie hover over, click, right-click) and then what you want to happen.