hardcoded names in percussion notation?

[jboogie]

Hi, I'm very new to lilypond and trying to hack my way to a
score for a small brazilian percussion ensemble. Actually the visive
output is fine for now, there's just one piece of code I don't
understand. 

To achieve a staff with two lines for an agogo bell, I used the example
for woodblocks in the "Common notation for percussions" manual section:


#(define agogo '((hiwoodblock default #t  2)
                   (lowoodblock default #t -2)))

agogostaff = {
  \set DrumStaff.instrumentName = #"Agogo"
  \override DrumStaff.StaffSymbol #'line-positions = #'(-2 2)
  \set DrumStaff.drumStyleTable = #(alist->hash-table agogo)
  \override Staff.BarLine #'bar-size = #3
}

\new DrumStaff {
  \agogostaff
  \drummode {
    \time 2/4
    wbl8 wbl16 wbl wbh8-> wbl |
    wbl8 wbl16 wbh-> ~ wbh wbl16 r8 |
  }
}


This works and produces the desired output. What I don't understand is
if "hiwoodblock", "lowoodblock", "wbl" and "wbh" are hardcoded, or if I
can change them, and if yes how?

cheers,
renato