<?php
$text='<div class="mce-toc">
<ul>
<li><a href="#mcetoc_1cfumeivr2t">Переменные</a>
<ul>
<li><a href="#mcetoc_1cfumeivr2u">Копирование переменных</a></li>
<li><a href="#mcetoc_1cfumeivr2v">Типы переменных</a>
<ul>
...
</div>';
$pattern = '/<div class="mce-toc">((\s|.)*?)<\/div>/';
// your code goes here
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