Truncate_and_strip tag of search extension

Hy everybody,
in my radiant site I’m using the search extension and it’s works very
I’ve tried to use the <r:truncate_and_strip [length=“100”] /> tag but I
don’t understand very well how does it work.
I need to display a snippet of the found pages and i tried this piece of


but it dosen’t work very well.
Can someone explain me how does this tag works maybe with a small

Thanks and greatings