[Zope] filtering results

Hi, I am a Zope newbie. I apologize if the terminology I use below is not correct, but I hope that you get the gist of what I am about to ask. I would like to be able to 'filter' results before returning them to the user. In other words, if a user requests a given object, it is passed through a filter before being passed on to him or her. As a simple example, I may want to tidy the html before the user sees it, or eliminate or add certain tags or words. I have put together a simple 'html tidy' external method that takes raw html and produces a tidied version, but I don't know how I can apply it. Thank you for any comments, suggestions, or simple examples you may be able to provide. Best Regards, gyro