aligning text in text spanner

[Martín Rincón Botero]

Hello, the following code produces text on both sides of the spanner that looks vertically well aligned with the upper limit of its box instead of the inferior one:

{
  f'1
  ~
  - \tweak style #'line
  - \tweak bound-details.left.stencil-align-dir-y #CENTER
  - \tweak bound-details.right.arrow ##t
  - \tweak bound-details.right.stencil-align-dir-y #CENTER
  - \tweak bound-details.left.text \markup \normal-text "ord."
  - \tweak bound-details.right.text \markup \normal-text "s.p."
  \startTextSpan
  f'1
  :32
  \stopTextSpan
}

produces

where the "s.p." vertically aligns well with the upper end of the "d" in "ord.". How can I achieve the opposite? Namely, that the "s.p." (or the "p") aligns with the bottom of "ord." so that it looks centered?

—Martín.

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