How to use regular rules to add navigation directory to articles in PHP

There may be many children who are interested in directory navigation. Click on the directory text above to quickly jump to related content, which is suitable for long articles or articles with special needs. Through regular expressions, the article content automatically extracts text with H2 tags for directory indexing.

$str = &#39;<h2 class="archt"><strong>我是里面的内容</strong></h2><h2 class="archt2">我是第2个内容</h2><strong>我没有h2包在里面</strong>&#39;;
preg_match_all(&#39;/<h2.*?>.*?(<[^>]+>)?([^<]+)(<\/[^>]+>)?<\/h2>/s&#39;, $str, $arr);
print_r($arr);

 Array(
    [0] => Array
        (
            [0] => <h2 class="archt">
<strong>我是里面的内容</strong></h2>
            [1] => <h2 class="archt2">我是第2个内容</h2>
        )

    [1] => Array
        (
            [0] => <strong>
            [1] => 
        )

    [2] => Array
        (
            [0] => 我是里面的内容
            [1] => 我是第2个内容
        )

    [3] => Array
        (
            [0] => </strong>
            [1] => 
        )

)

Write it as a function

function article_index($content){  
    $matches = array();   
    $ul_li = &#39;&#39;;    $r = &#39;/<h2.*?>.*?(<[^>]+>)?([^<]+)(<\/[^>]+>)?<\/h2>/s&#39;;    if(preg_match_all($r, $content, $matches))
    {        foreach($matches[2] as $num => $title)
        {            $ul_li .= &#39;<em>&#39;.$title." </em>";
        }   
    }   
    return $ul_li;
}

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