Implement remaining "in select" tags

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

@@ -1152,7 +1152,7 @@ private function step_in_body() {
 	 *
 	 * @throws WP_HTML_Unsupported_Exception When encountering unsupported HTML input.
 	 *
-	 * @see https://html.spec.whatwg.org/#parsing-main-inbody
+	 * @see https://html.spec.whatwg.org/multipage/parsing.html#parsing-main-inselect
 	 * @see WP_HTML_Processor::step
 	 *
 	 * @return bool Whether an element was found.
@@ -1163,6 +1163,16 @@ private function step_in_select() {
 		$op       = "{$op_sigil}{$tag_name}";
 
 		switch ( $op ) {
+			/*
+			 * > A start tag whose tag name is "html"
+			 */
+			case '+HTML':
+				$this->last_error = self::ERROR_UNSUPPORTED;
+				throw new WP_HTML_Unsupported_Exception( "Cannot process {$tag_name} element." );
+
+			/*
+			 * > A start tag whose tag name is "option"
+			 */
 			case '+OPTION':
 				$current_node = $this->state->stack_of_open_elements->current_node();
 				if ( $current_node && 'OPTION' === $current_node->node_name ) {
@@ -1171,7 +1181,12 @@ private function step_in_select() {
 				$this->insert_html_element( $this->state->current_token );
 				return true;
 
+			/*
+			 * > A start tag whose tag name is "optgroup"
+			 * > A start tag whose tag name is "hr"
+			 */
 			case '+OPTGROUP':
+			case '+HR':
 				$current_node = $this->state->stack_of_open_elements->current_node();
 				if ( $current_node && 'OPTION' === $current_node->node_name ) {
 					$this->state->stack_of_open_elements->pop();
@@ -1186,6 +1201,9 @@ private function step_in_select() {
 				$this->insert_html_element( $this->state->current_token );
 				return true;
 
+			/*
+			 * > An end tag whose tag name is "optgroup"
+			 */
 			case '-OPTGROUP':
 				$walker = $this->state->stack_of_open_elements->walk_up();
 				$current_node = $walker->current();
@@ -1206,6 +1224,9 @@ private function step_in_select() {
 				}
 				return $this->step();
 
+			/*
+			 * > An end tag whose tag name is "option"
+			 */
 			case '-OPTION':
 				$current_node = $this->state->stack_of_open_elements->current_node();
 				if ( $current_node && 'OPTION' === $current_node->node_name ) {
@@ -1214,7 +1235,12 @@ private function step_in_select() {
 				}
 				return $this->step();
 
+			/*
+			 * > An end tag whose tag name is "select"
+			 * > A start tag whose tag name is "select"
+			 */
 			case '-SELECT':
+			case '+SELECT':
 				if ( ! $this->state->stack_of_open_elements->has_element_in_select_scope( 'SELECT' ) ) {
 					return $this->step();
 				}