Staffgroup question

[Jeffery B. Rancier]

Hi All.

I've been fiddling with the satb.ly template, trying to create a
barbershop quartet template.  My question: Why can I get away with
specifying the time signature once in the first staff, and have it
default to the same in the lower staff, but not have the key signature
behave the same way.  It may seem a silly question, but I never played
anything that has diffent keys in a connected staff.  As such:

[...]

\score { \notes
         \context StaffGroup <<
             \property Score.automaticMelismata = ##t
             \context Lyrics = tenorLyrs {  }
             \context Staff = treble { \key ef \major \time 2/2 }
             \context Lyrics = leadLyrs {  }
             \context Lyrics = bariLyrs {  }
             \context Staff = bass {\clef bass \key ef \major }
             \context Lyrics = bassLyrs {  }

             \addlyrics
             \context Staff = treble \context Voice = VA { \voiceOne 
\tenorMusic }
             \context Lyrics = tenorLyrs { \tenorWords}
             \addlyrics
             \context Staff = treble \context Voice = VB { \voiceTwo \leadMusic 
}
             \context Lyrics = leadLyrs { \leadWords}
             \addlyrics
             \context Staff = bass \context Voice = VA { \voiceOne \bariMusic }
             \context Lyrics = bariLyrs { \bariWords}
             \addlyrics
             \context Staff = bass  \context Voice = VB { \voiceTwo \bassMusic }
             \context Lyrics = bassLyrs { \bassWords}
         >>

[...]

And secondly, is that the correct place(s) to put the \key & \time
keywords?  Thirdly, the original template defined:

,----
|            \context Lyrics = tenorLyrs {  }
`----

as

,----
|            \context Lyrics = tenorLyrs { s1 }
`----

What's the significance of that term? And finally, is there a
hierarchical diagram of which contexts are valid where?  Or perhaps an
EBNF?  I've been kinda randomly trying spots (and yes, I did read).

Thanks in advance, sorry for the greenhorn questions.

-- 
Thanks,
Jeff