fix(core): let makeSections xpath query cope with multiple classes (#733

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* Let makeSections xpath query cope with multiple classes

As-of https://gerrit.wikimedia.org/r/c/mediawiki/core/+/939783 in mediawiki-core, this class attribute is going to contain multiple classes. This would break the section-creation. This change to the query is backwards-compatible, so this should just inoculate the skin against future updates.

* Shorten line for mediawiki-lint compatibility

* fix: update html selector for parser output

Related: T350627

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Co-authored-by: alistair3149 <alistair3149@users.noreply.github.com>

includes/Partials/BodyContent.php

@@ -132,7 +132,10 @@ private function getHeadingName( $node ) {
 	 */
 	private function makeSections( DOMDocument $doc, array $headingWrappers ) {
 		$xpath = new DOMXpath( $doc );
-		$containers = $xpath->query( '//div[@class="mw-parser-output"][1]' );
+		$containers = $xpath->query(
+			// Equivalent of CSS attribute `~=` to support multiple classes
+			'//div[contains(concat(" ",normalize-space(@class)," ")," mw-parser-output ")][1]'
+		);
 
 		// Return if no parser output is found
 		if ( !$containers->length || $containers->item( 0 ) === null ) {