Does two TextSpanners require two voices?

[Bernardo Barros]

Hi List,

Can I have two simultaneous text spanners with different reference
points at the same time?
Does two text spanner require two voices like this?

{
<<
  {
    \override TextSpanner #'(bound-details left text) = #"bla"
    \override TextSpanner #'(bound-details right text) = #"blu"
    a'4 \startTextSpan
    b'4 c''
    b'4 \stopTextSpan
  }
  \\
  {
    \override TextSpanner #'(bound-details left text) = #"ble"
    \override TextSpanner #'(bound-details right text) = #"bli"
    s4 \startTextSpan
    s4
    s2 \stopTextSpan
  }
>>
}