In trying to break apart SB programming I'm trying to understand a few things. Mainly right now, looking the main source macros.

There's a subpage called "SOURCE LIST ZONE 1", each of the source buttons has a join and the logic it has is "FAMILY ROOM AVR->TWO ZONE VOLUME EXTENDER->SOURCE SELECT LINE 1"

The next would be LINE 2, LINE 3, etc

There is also a subpage labeled "ZONE 1". that page has buttons each button has a source on it. These buttons each seem to have the switching logic on them. For example one button says DVD/CD the logic is:
2s delay
Two zone extended-> extended source select
2s delay
Family-> avr-> cd/DVD
Family, sanding tv -> component 2

So what is the first line, "extender source select" doing?

Also, are these buttons the "line 1" "line 2" etc from the first subpage?