HTML API: Add select handling

src/wp-includes/html-api/class-wp-html-open-elements.php

@@ -189,11 +189,6 @@ public function current_node_is( string $identity ): bool {
 	/**
 	 * Returns whether an element is in a specific scope.
 	 *
-	 * ## HTML Support
-	 *
-	 * This function skips checking for the termination list because there
-	 * are no supported elements which appear in the termination list.
-	 *
 	 * @since 6.4.0
 	 *
 	 * @see https://html.spec.whatwg.org/#has-an-element-in-the-specific-scope
@@ -311,19 +306,38 @@ public function has_element_in_table_scope( $tag_name ) {
 	/**
 	 * Returns whether a particular element is in select scope.
 	 *
-	 * @since 6.4.0
+	 * This test differs from the others like it, in that its rules are inverted.
+	 * Instead of arriving at a match when one of any tag in a termination group
+	 * is reached, this one terminates if any other tag is reached.
 	 *
-	 * @see https://html.spec.whatwg.org/#has-an-element-in-select-scope
+	 * > The stack of open elements is said to have a particular element in select scope when it has
+	 * > that element in the specific scope consisting of all element types except the following:
+	 * >   - optgroup in the HTML namespace
+	 * >   - option in the HTML namespace
 	 *
-	 * @throws WP_HTML_Unsupported_Exception Always until this function is implemented.
+	 * @since 6.4.0 Stub implementation (throws).
+	 * @since 6.7.0 Full implementation.
+	 *
+	 * @see https://html.spec.whatwg.org/#has-an-element-in-select-scope
 	 *
 	 * @param string $tag_name Name of tag to check.
-	 * @return bool Whether given element is in scope.
+	 * @return bool Whether the given element is in SELECT scope.
 	 */
 	public function has_element_in_select_scope( $tag_name ) {
-		throw new WP_HTML_Unsupported_Exception( 'Cannot process elements depending on select scope.' );
+		foreach ( $this->walk_up() as $node ) {
+			if ( $node->node_name === $tag_name ) {
+				return true;
+			}
 
-		return false; // The linter requires this unreachable code until the function is implemented and can return.
+			if (
+				'OPTION' !== $node->node_name &&
+				'OPTGROUP' !== $node->node_name
+			) {
+				return false;
+			}
+		}
+
+		return false;
 	}
 
 	/**