See https://bugs.webkit.org/show_bug.cgi?id=145599#c10 As of ES6, source/multiline/ignoreCase/global should all be accessor functions on `RegExp.prototype`, and not data properties on each instance. Before `RegExp#flags` can land in #145599, the code in RegExpObject needs to be fixed to convert these to accessor functions.
*** This bug has been marked as a duplicate of bug 145705 ***