Prefilters/Postfilters预滤器/后滤器

Prefilter and postfilter plugins are very similar in concept; where they differ is in the execution -- more precisely the time of their execution.
从概念上看，预滤器和后滤器插件都很简单；不同之处就在于它们的执行，更确切地说是它们的执行时刻（非时间段，而是某一个时刻）。

Prefilters are used to process the source of the template immediately before compilation. The first parameter to the prefilter function is the template source, possibly modified by some other prefilters. The plugin is supposed to return the modified source. Note that this source is not saved anywhere, it is only used for compilation.
预滤器用来在编译之前直接处理模板源文件。预滤器函数的第一个参数是模板源文件，该文件可能被其他一些预滤器修正过。此预滤器插件将返回修正过的源文件。请记住此源文件仅用来编译，它不会在任何地方被保存。

Postfilters are used to process the compiled output of the template (the PHP code) immediately after the compilation is done but before the compiled template is saved to the filesystem. The first parameter to the postfilter function is the compiled template code, possibly modified by other postfilters. The plugin is supposed to return the modified version of this code.
后滤器用来在编译之后直接处理模板的编译输出（PHP代码），但须在编译之后的模板被保存到文件系统之前就进行操作。预滤器函数的第一个参数是编译之后的模板代码，该代码可能被其他一些后滤器修正过。此后滤器插件将返回修正过的代码文件。

<?php
/*
 * Smarty plugin
 * -------------------------------------------------------------
 * File:     prefilter.pre01.php
 * Type:     prefilter
 * Name:     pre01
 * Purpose:  Convert html tags to be lowercase.
 * -------------------------------------------------------------
 */
 function smarty_prefilter_pre01($source, &$smarty)
 {
     return preg_replace('!<(\w+)[^>]+>!e', 'strtolower("$1")', $source);
 }
?>

<?php
/*
 * Smarty plugin
 * -------------------------------------------------------------
 * File:     postfilter.post01.php
 * Type:     postfilter
 * Name:     post01
 * Purpose:  Output code that lists all current template vars.
 * -------------------------------------------------------------
 */
 function smarty_postfilter_post01($compiled, &$smarty)
 {
     $compiled = "<pre>\n<?php print_r(\$this->get_template_vars()); ?>\n</pre>" . $compiled;
     return $compiled;
 }
?>