BarNumber 'break-visibility

[Andrew Black - lists]

I am a little confused by the following :

         \override Score.BarNumber #'break-visibility = ##(#f #t #t)
         \override Score.BarNumber #'break-visibility
           = #end-of-line-invisible

 - what is the default for before you tweak
 - by setting end-of-line-invisible do  I set the other places _visible_

I want to put bar numbers every 5 I have successfully done  but will be 
more likely to remember it if I understand the thinking behind it.

I have looked at 
http://lilypond.org/doc/v2.11/Documentation/user/lilypond/Bar-numbers#Bar-numbers 
but still am confused.