\header {

  texidoc = "Horizontal spacing is bounded by the current measure length.
This means that the 3/8 setting does not affect the whole rest spacing." 

}


\version "2.12.0"

\layout {
  ragged-right = ##t
}

\score {
  \new Staff \with {
    \remove Separating_line_group_engraver
  } {
    \relative c' {
      \override Score.SpacingSpanner #'uniform-stretching = ##t
      \set Score.proportionalNotationDuration = #(ly:make-moment 4 25)
      r1
      \time 3/8 r4.
    }
  }
}