5.3.2 \set and \unset

The \set command syntax is

\set context.property = value

where value must be preceded by the ‘#’ character if it is a Scheme object.

The counterpart command \unset’s syntax is

\unset context.property

This removes a previously set definition of the property from the context. Any properties that have been set in an enclosing context are not altered by an \unset in the same enclosed context.

For example, multi-measure rests are combined into a single bar (as explained in Compressing empty measures) if the context property skipBars is set to #t:

R1*2
\set Score.skipBars = ##t
R1*2

If the context argument is left out, then the property is set in the current ‘bottom’ context (typically ChordNames, Voice, TabVoice, or Lyrics).

<<
  \set Score.autoBeaming = ##f
  \relative {
    e''8 e e e
    \set autoBeaming = ##t
    e8 e e e
  } \\
  \relative {
    c''8 c c c c8 c c c
  }
>>

Note that the bottom context may not always contain an engraver that uses the property that you wish to change. For example, attempting to set the skipBars property of the default, bottom context has no effect because it is a property of the Score, not Voice context.

R1*2
\set skipBars = ##t
R1*2

Contexts are hierarchical; any change specified for an enclosing context (e.g., Staff) would also apply to all Voices in that current Staff context (assuming, of course, that the Voice context didn’t have an override of its own).

All contexts inherit settings established in the top-most Global context (via \grobdescriptions), although a few of those defaults get overridden in their own context definitions.

<<
  \set Score.autoBeaming = ##t
  \relative {
    \unset autoBeaming
    e''8 e e e
    \unset Score.autoBeaming
    e8 e e e
  } \\
  \relative {
    c''8 c c c c8 c c c
  }
>>

Like \set, the context argument does not have to be specified for a bottom context, so the two statements

\set Voice.autoBeaming = ##t
\set autoBeaming = ##t

are equivalent if the current bottom context is Voice.

As described above, \unset restores the default value of a context property. However, it is sometimes useful to change a value for some time, then returning to the previously used value. For this purpose, there are the two commands \pushContextProperty and \popContextProperty: the first one pushes the current value to a stack and sets a new value, while the second one pops off the value from the stack and uses it to restore the previous value.

{
  c'
  \pushContextProperty Staff.fontSize 3
  c'
  \pushContextProperty Staff.fontSize 6
  c'
  \popContextProperty Staff.fontSize
  c'
  \popContextProperty Staff.fontSize
  c'
}