Tailoring Triangulation

This is Palanirajan from India, I am working in MX for the past two years, i have some queries regarding triangulation,

I had come across this option of Tailoring Triangulation which means an area of points can be isolated from triangulation with the use of PBRK string, we have to create a boundary around the area which we want to isolate and name it as PBRK String

Got this information from MX Help Application

I have tried this option, but it is not working, can i have your views on this