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<?php $re = '~(?:<p>(?=[^<>]*</p>)|\G(?!^))[^\d<>]*\d+\K\h~'; $str = '<p>My 90 days 123 work.</p>'; echo preg_replace($re, "&nbsp", $str);
Output for 8.0.1 - 8.0.30, 8.1.0 - 8.1.34, 8.2.0 - 8.2.30, 8.3.0 - 8.3.30, 8.4.1 - 8.4.18, 8.5.0 - 8.5.3
<p>My 90&nbspdays 123&nbspwork.</p>

preferences:
87.99 ms | 1108 KiB | 4 Q