JDK-8007619 has added support for non-standard RegExp constructor properties, but there are some compatibility issues:

 - Properties should be defined as constants but currently are handled via __noSuchProperty__ and thus easy to override
 - Not the whole set of properties is supported (leftContext, rightContext, multiline are missing)
 - Properties are handled though a hidden property in RegExp constructor which can be accessed and modified by scripts
 - Properties behaviour differs from Spidermonkey and V8 regarding default value, when they are set, etc.