https://bugzilla.mozilla.org/show_bug.cgi?id=1730289
1730289 - Intermittent [tier 2] selection/splitText-normalize.html ==...
RESOLVED (nobody) in Core - DOM: Selection. Last updated 2022-08-31.
intermittenttierselectionsplittextnormalize
https://www.php.net/manual/it/domtext.splittext.php
PHP: DOMText::splitText - Manual
Breaks this node into two nodes at the specified offset
phpsplittextmanual