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<?php $string = "<tag>i don't know what is here</tag>"; $replacement = "replacement"; $doc = new DOMDocument(); $doc->loadXML($string); $node = $doc->getElementsByTagName('tag')->item(0); $newNode = $doc->createElement("tag", $replacement); $node->parentNode->replaceChild($newNode, $node); echo $doc->saveHTML();
Output for 7.1.25 - 7.1.33, 7.2.0 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.27, 8.2.0 - 8.2.17, 8.3.0 - 8.3.4
<tag>replacement</tag>

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167.89 ms | 403 KiB | 175 Q