As simple as:

R1 * 3/4

Read a whole-bar rest. Which is 4 quarter notes. 4 quarter notes divided by 4, times by 3 is a whole-bar rest in 3/4 time!

As simple as:

R1 * 3/4

Read a whole-bar rest. Which is 4 quarter notes. 4 quarter notes divided by 4, times by 3 is a whole-bar rest in 3/4 time!

Edit TLTR

They are not whole-note rests, either in 3/4 or 4/4 time but whole-bar rests, to be clear. They have a default value of 4 quarters.

My way

Larger than 4 quarter-notes: 5/4 is R1 * 5/4
Equal to 4 quarter-notes: 4/4 is R1 * 1/1, simply R1
Smaller than 4 quarter-notes: 3/4 time is R1 * 3/4

The fraction mirrors the time signature.

I'm seeing it as a whole-bar is 100%, more than 4 quarters is more than 100%, less than 4 quarters is less than 100%.

While the documentation is of course correct and doesn't state the fraction way, apart from larger than 4 quarter-notes,(and @Aaron's answer should probably be the correct answer), I think there are valid reasons for using fractions:

• fraction mirrors the time signature
• introduces the fraction of a note concept early-on in learning lilypond, it's particularly used in:
  • tuplets e.g. \tuplet 3/2 { c8 c c} (but this is 3 in space of 2, not tech. a fraction)
  • placement of delayed ornaments e.g { c8 * 1/4 s\trill s\turn s\prall d8 }
  • other places like spacing
• confusion: if I see 2, I expect to see a half-note not a whole-note (half-notes have the additional pain of looking like whole-notes). With 1 I'm always seeing whole-note symbol.