Rubicon Express Brake Line Question, Yes I feel Dumb..

I have been lurking for a while and just wanted to say hi. This is probably a stupid question but here goes. I just bought a Rubicon Express BB that came with an extended 18" brake line. Does anyone have any idea what this is supposed to replace? Sorry Im a former TJ (I have had 2 of them) guy who has bought his first XJ :confused1 so this is all pretty new. In case it matters it's a 2001 Cherokee sport.

Thanks!!

It replaces the line going to the rear brakes. It T's on the driver side of the rear axle, right on top of the housing and conects up along the driver side to the unibody.