Does "ie8_length" reliably identify the UA as IE8?

I notice that, under IE8 (8.0.6001.18702), there is an array attribute called "ie8_length" which very often looks to be equal to "length." True when compatibility mode is either on or off.

Is the presence of this little guy a reliable tell that the UA is indeed IE8? And, in its absence, can I 开发者_JAVA百科believe that the UA is not IE8?

Thanks!