It is asphalt that is "Modified" with a plastic or rubber to make it more flexible, and then reinforced with a fabric. 

Having said that, you want to make sure the doors/jambs are reinforced among many other things.

The mess is used for areas with alot of movement,it is an reinforcer.

have to reinforce the sub floor as well I have had them fall right through the sub floor.

When you ask (old) people about what hasn't worked it will re-inforce a better more effective approach you read in a book. 

I found that most I attended taught me something, or at least reinforced something.  

This reinforces my statement.Terry

People do weird things all the time in old houses to reinforce sagging roofs or floors that dont actually transfer load to the foundation but visually cure the problem.

This will help clarify and reinforce what you are reading.

Well this is called "reinforcing"I use analogy of a rope and TUG OF WAR and there is a line to be pulled over.The sellers on one side and you're on the other, and most negotiations it's tug of war.Well I don't want to be a tug-of-war.I want them to pull me on their side, I don't want to pull them to my sideThis "reinforcing" helps them pull me to their side.There's another reason for this, this a nontraditional outside the box kind of solution, and I want to prepare them the sellers to be talking to their friends about what they're doing with their house.