Use this to dynamically register prefilters to run templates
through before they are compiled. See template prefilters for
more information on how to setup a prefiltering function.
注册一个在模板编译之前执行的预过滤器。如何设立预过滤函数，请查看模板预过滤器。
The php-function callback function
can be either (a) a string containing the function name or (b) an array
of the form array(&$object, $method) with
&$object being a reference to an object
and $method being a string containing the
mehod-name or (c) an array of the form array(&$class,
$method) with $class being a classname
and $method being a class method of that
class.
执行函数的格式可以是一个包含函数名称的字符串；也可以是一个array(&$object, $method)数组形式，其中&$object是一个对象的引用，而$method是它的一个方法；还可以是一个array(&$ class, $method)数组形式，其中$class是一个类的名称，$method是类中的一个方法。