According to MDN here and here, it says that the readystatechange event is supported in all browsers, but the document.readyState property is only supported back until around IE9+ (8*).
This doesn't really make sense, given that literal definition of the readystatechange event is:
The readystatechange event is fired when the readyState attribute of a document has changed.
Unless previous implementations of readystatechange keep document.readyState as an internal variable that can't be accessed. Is this the case, or is this simply a documentation error?
