2.21.1 change of behavior of \compressMMRests?

[Paul Scott]

The following MWE is a variation of the first code example in 2.21.1 
Notation manual 1,2,2 Full Measure
Rests:

% Rest measures contracted to single measure

\score{
  \new Staff \new Voice
  << { \compressMMRests } { R1*4 R1*24 R1*4 b'2^"Tutti" b'4 a'4} >>
}

mmxtest.ly:13:25: error: syntax error, unexpected '}', expecting \header

I believe this used to work In 2.19.xx.

How can I accomplish the following, i.e. have the structure common to 
all parts in a single definition as I have been doing for many years 
with Lily?

For example:

\version 2.20.0"

timing = { \compressMMRests s1*28 \bar "|." }

PartA = { R1*4 R1*24 }

PartAComplete = << \timing \PartA >>

\score{ \new Staff \new Voice \PartAComplete }