dynamic spanner help

[James E. Bailey]

Also, the \crescTextCresc and \dimTextDim work like there's a \once in  
front of them when they're in the variable.
\version "2.11.51"
\layout {
   \context {
      \type "Engraver_group"
      \name VocalDynamics
      \alias Voice
      \consists Text_engraver
      \consists "Dynamic_engraver"
      \consists "Text_engraver"
      \override TextScript #'font-shape = #'italic
   }
   \context {\Staff \accepts VocalDynamics}
}
Voice = \relative { e1 f g e a g f d }
VoiceDynamics = \new VocalDynamics {
   \override DynamicTextSpanner #'dash-period = #-1.0
   \dimTextDim
   s1*3\> s1\!
   \crescTextCresc
   s1*3\< s1\!
   \setHairpinDim
}
AlternateDynamics = \new VocalDynamics {
   \dimTextDim
   s1 s\> s s\!
   s1 s\> s s\!
}

\score {
   \new Staff << \VoiceDynamics \Voice>>
   \layout {}
}
\score {
   \new Staff << \AlternateDynamics \Voice >>
   \layout {}
}

\relative c'' {
       \override DynamicTextSpanner #'dash-period = #-1.0
       \crescTextCresc
       c1\< | d | b | c\!
       c\< d b c\!
}