钩子
===
在模版文件中经常看到调用钩子的用法
如：
```html
<!--{hook/global_usernav_extra2}-->
```
这行代码在模版解析文件中会如此解析：
```php
$template = preg_replace("/\{hook\/(\w+?)(\s+(.+?))?\}/ie", "\$this->hooktags('\\1', '\\3')", $template);
```
可以看到是直接调用$this->hooktags方法，那hooktags是怎么定义的呢？请看：
```php
function hooktags($hookid, $key = '') {
global $_G;
$i = count($this->replacecode['search']);
$this->replacecode['search'][$i] = $search = "<!--HOOK_TAG_$i-->";
$dev = '';
if(isset($_G['config']['plugindeveloper']) && $_G['config']['plugindeveloper'] == 2) {
$dev = "echo '<hook>[".($key ? 'array' : 'string')." $hookid".($key ? '/\'.'.$key.'.\'' : '')."]</hook>';";
}
$key = $key !== '' ? "[$key]" : '';
$this->replacecode['replace'][$i] = "<?php {$dev}if(!empty(\$_G['setting']['pluginhooks']['$hookid']$key)) echo \$_G['setting']['pluginhooks']['$hookid']$key;?>";
return $search;
}
```
