Cache Groups
      You can do more elaborate grouping by setting up cache_id groups. This is
      accomplished by separating each sub-group with a vertical bar "|" in the
      cache_id value. You can have as many sub-groups as you like.
     
      You can think of cache groups like a directory hierarchy. For instance, a
      cache group of "a|b|c" could be thought of as the directory structure
      "/a/b/c/". clear_cache(null,"a|b|c") would be like removing the files
      "/a/b/c/*". clear_cache(null,"a|b") would be like removing the files
      "/a/b/*". If you specify a compile_id such as
      clear_cache(null,"a|b","foo") it is treated as an appended cache group
      "/a/b/c/foo/". If you specify a template name such as
      clear_cache("foo.tpl","a|b|c") then Smarty will attempt to remove
      "/a/b/c/foo.tpl". You CANNOT remove a specified template name under
      multiple cache groups such as "/a/b/*/foo.tpl", the cache grouping works
      left-to-right ONLY. You will need to group your templates under a single
      cache group heirarchy to be able to clear them as a group.
     
      Cache grouping should not be confused with your template directory
      heirarchy, the cache grouping has no knowledge of how your templates are
      structured. So for example, if you have a template structure like
      "themes/blue/index.tpl" and you want to be able to clear all the cache
      files for the "blue" theme, you will need to create a cache group
      structure that mimics your template file structure, such as
      display("themes/blue/index.tpl","themes|blue"), then clear them with
      clear_cache(null,"themes|blue").
     
| Example 14-9. cache_id groups | 
<?phprequire('Smarty.class.php');
 $smarty = new Smarty;
 
 $smarty->caching = true;
 
 // clear all caches with 'sports|basketball' as the first two cache_id groups
 $smarty->clear_cache(null,'sports|basketball');
 
 // clear all caches with "sports" as the first cache_id group. This would
 // include "sports|basketball", or "sports|(anything)|(anything)|(anything)|..."
 $smarty->clear_cache(null,'sports');
 
 // clear the foo.tpl cache file with "sports|basketball" as the cache_id
 $smarty->clear_cache('foo.tpl','sports|basketball');
 
 
 $smarty->display('index.tpl','sports|basketball');
 ?>
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