Beat grouping within a measure is controlled by the beatStructure
context property. Values of beatStructure are
established for many time signatures in file
scm/time-signature-settings.scm. Values of beatStructure
can be changed or set with \set.
Alternatively, \time can be used to both
set the time signature and establish the beat structure.
For this, you specify the internal grouping of beats in a measure
as a list of numbers (in Scheme syntax) before the time signature.
\time applies to the Timing context, so it will not
reset values of beatStructure or baseMoment that are set
in other lower-level contexts, such as Voice.
If the Measure_grouping_engraver is included
in one of the display contexts, measure grouping signs will be
created. Such signs ease reading rhythmically complex modern music.
In the example, the 9/8 measure is grouped in two different
patterns using the two different methods, while the 5/8 measure
is grouped according to the default setting in
scm/time-signature-settings.scm: