text spanning

[Hugh Myers]

The following fails twice over; it leaves out the indicated text and
ignores \textSpannerDown:

\version "2.13.7"

 upper = {
  c4 d e  \startTextSpan f % polyphonic
  g4 a b c % monophonic, see below
  b4 \stopTextSpan g e c % polyphonic again
 }

 lower = {
  c,2 g2 % polyphonic
  s1 % a spacer "disables" this voice tamporarily
  g2 c2 % and here we are again.
}

<<
  \new Staff \relative c'' {
    \textSpannerDown
    \override TextSpanner #'(bound-details left text) = "let ring "
    <<
      \new Voice = "1" { \voiceOne \upper }
      \new Voice = "2" { \voiceTwo \lower }
    >>
  }
  \new TabStaff \relative c' {
    <<
      \new TabVoice = "t1" { \voiceOne \upper }
      \new TabVoice = "t2" { \voiceTwo \lower }
    >>
  }
>>

Where did I screw up?

--hsm