Fully understanding D.2.4 template

[Tomas Valusek]

Hello,

I'm a piano teacher, so I'd like to understand what's the meaning of all 
the statements used in layout block of D.2.4 template. I'm going  to 
include it below, my questions are marked there.

    \version "2.9.13"
    upper = \relative c'' {
      \clef treble
      \key c \major
      \time 4/4
   
      a b c d
    }
   
    lower = \relative c {
      \clef bass
      \key c \major
      \time 4/4
   
      a2 c
    }
   
    dynamics = {
      s2\fff\> s4
      s\!\pp
    }
   
    pedal = {
      s2\sustainDown s2\sustainUp
    }
   
    \score {
      \new PianoStaff <<
        \new Staff = "upper" \upper
        \new Dynamics = "dynamics" \dynamics
        \new Staff = "lower" <<
          \clef bass
          \lower
        >>
        \new Dynamics = "pedal" \pedal
      >>
      \layout {
        \context {
          \type "Engraver_group"
          \name Dynamics
          \alias Voice % So that \cresc works, for example.
          \consists "Output_property_engraver"
   
          \override VerticalAxisGroup #'minimum-Y-extent = #'(-1 . 1) % 
??? How to change distance between \upper and \lower staves?
          pedalSustainStrings = #'("Ped." "*Ped." "*")
          pedalUnaCordaStrings = #'("una corda" "" "tre corde")
   
          \consists "Piano_pedal_engraver"
          \consists "Script_engraver"
          \consists "Dynamic_engraver"
          \consists "Text_engraver"
   
          \override TextScript #'font-size = #2
          \override TextScript #'font-shape = #'italic
          \override DynamicText #'extra-offset = #'(0 . 2.5) % ???
          \override Hairpin #'extra-offset = #'(0 . 2.5) % ???
   
          \consists "Skip_event_swallow_translator" % ???
   
          \consists "Axis_group_engraver" % ???
        }
        \context {
          \PianoStaff
          \accepts Dynamics
          \override VerticalAlignment #'forced-distance = #7 % ??? How 
to change distance between \upper and \lower staves?
        }
      }
    }
    \score {
      \new PianoStaff <<
        \new Staff = "upper" << \upper \dynamics >>
        \new Staff = "lower" << \lower \dynamics >>
        \new Dynamics = "pedal" \pedal
      >>
      \midi {
        \context {
          \type "Performer_group"
          \name Dynamics
          \consists "Piano_pedal_performer"
        }
        \context {
          \PianoStaff
          \accepts Dynamics
        }
      }
    }


One more question arises: How to extend this template to include solo 
instrument with smaller staff? (Maybe template D.2.5.)

Tomas Valusek