The libxml extension is needed for DOMDocument.

johnbillion · johnbillion · commit aa4ca214515c · 2022-06-03T15:46:35.000+02:00
diff --git a/composer.json b/composer.json
@@ -21,6 +21,7 @@
 	],
 	"require": {
 		"php": ">=7",
+		"ext-libxml": "*",
 		"johnbillion/wp-parser-lib": "^1.3.0"
 	},
 	"require-dev": {
