filter(static fn (DOMNameSpaceNode $node): bool => $node->namespaceURI !== Xmlns::xml()->value()) ->reduce( /** * @param list $grouped * @return list */ static fn (array $grouped, DOMNameSpaceNode $node): array => values(unique([...$grouped, $node->namespaceURI])), [] ); foreach (sort($namespaceURIs) as $index => $namespaceURI) { rename($document, $namespaceURI, $prefix . ((string) ($index+1))); } }