text-script-engraver error

[chip]

I am trying to use the slash note heads with the example from the manual
and get the following error:

Parsing...
error: unknown translator: `Text_script_engraver'

here is the code:

\context {
    \name ImproVoice
    \type "Engraver_group_engraver"
    \consists "Note_heads_engraver"
    \consists "Text_script_engraver"
    \consists Pitch_squash_engraver
    squashedPosition = #0
    \override NoteHead #'style = #'slash
    \override Stem #'transparent = ##t
    \alias Voice
         }
  \context {
    \StaffContext
    \accepts ImproVoice    
  }

I don't see anything in that section of the manual about needing to
include any files, such as 'english.ly' for example.

I am using version 2.2.2
What must I do to make this work?
Thanks,
chip