Template prefilters are PHP functions that your templates are ran through before they are compiled. This is good for preprocessing your templates to remove unwanted comments, keeping an eye on what people are putting in their templates, etc. Prefilters can be either registered or loaded from the plugins directory by using load_filter() function or by setting $autoload_filters variable. Smarty will pass the template source code as the first argument, and expect the function to return the resulting template source code.
Example 15-2. using a template prefilter