When the ScriptEngineMajorVersion function is called, it returns a value that identifies the major revision level of the implementation, not the revision level of the ECMAScript or JavaScript language specification that is currently supported by the implementation.

An implementation of Internet Explorer ECMAScript that supports distinct document modes (that separately implement other versions of the language, such as JScript 5.7 and JScript 5.8 functionality) can return a single value that does not vary among modes. The return value cannot be used as a reliable indicator of the availability or lack of availability of specific language features.

The ECMAScript implementations within Internet Explorer 9 always return a value of 9, even when Internet Explorer 9 is operating in Quirks, IE7, or IE8 document modes.