The usage is isIE.browser a property that returns a boolean and relies on conditional comments the method isIE.detectedVersion() which returns a number between 5 and 10. I am making the assumption that anything lower than 6 and you are in serious old school territory and you will something more beefy than a one liner and anything higher than 10 and you are in to newer territory. I have read something about IE11 not supporting conditional comments but I've not fully investigated, that is maybe for a later date.