Add explanatory comments and update ticket number.

Co-authored-by: Weston Ruter <westonruter@git.wordpress.org>
Co-authored-by: Jon Surrell <jonsurrell@git.wordpress.org>

Author: 3 people

src/wp-includes/html-api/class-wp-html-processor.php

@@ -633,6 +633,16 @@ private function step_in_body() {
 			$this->reconstruct_active_formatting_elements();
 
 			$current_token = $this->bookmarks[ $this->state->current_token->bookmark_name ];
+
+			/*
+			 * > A character token that is U+0000 NULL
+			 *
+			 * Any successive sequence of NULL bytes is ignored and won't
+			 * trigger active format reconstruction. Therefore, if the text
+			 * only comprises NULL bytes then the token should be ignored
+			 * here, but if there are any other characters in the stream
+			 * the active formats should be reconstructed.
+			 */
 			if (
 				1 <= $current_token->length &&
 				"\x00" === $this->html[ $current_token->start ] &&

tests/phpunit/tests/html-api/wpHtmlSupportRequiredActiveFormatReconstruction.php

@@ -17,9 +17,7 @@ class Tests_HtmlApi_WpHtmlSupportRequiredActiveFormatReconstruction extends WP_U
 	 * Ensures that active formats are properly reconstructed when visiting text nodes,
 	 * verifying that the proper breadcrumbs are maintained when scanning through HTML.
 	 *
-	 * @ticket {TICKET_NUMBER}
-	 *
-	 * @since 6.5.0
+	 * @ticket 60455
 	 */
 	public function test_reconstructs_active_formats_on_text_nodes() {
 		$processor = WP_HTML_Processor::create_fragment( '<p><b>One<span><p>Two' );
@@ -41,6 +39,12 @@ public function test_reconstructs_active_formats_on_text_nodes() {
 		 * second text node but fail to reconstruct the implicitly-closed B element.
 		 * The other way is to fail to abort when encountering the second text node
 		 * because the kind of active format reconstruction isn't supported.
+		 *
+		 * At the time of writing this test, the HTML Processor bails whenever it
+		 * needs to reconstruct active formats, unless there are no active formats.
+		 * To ensure that this test properly works once that support is expanded,
+		 * it's written to verify both circumstances. Once support is added, this
+		 * can be simplified to only contain the first clause of the conditional.
 		 */
 
 		if ( $processor->next_token() ) {