### 5.3.3 The `\override` command

There is a special type of context property: the grob description. Grob descriptions are named in `StudlyCaps` (starting with capital letters). They contain the ‘default settings’ for a particular kind of grob as an association list. See ‘`scm/define-grobs.scm`’ to see the settings for each grob description. Grob descriptions are modified with `\override`.

The syntax for the `\override` command is

>     \override [context.]GrobName.property = #value

For example, we can increase the thickness of a note stem by overriding the `thickness` property of the `Stem` object:

>     c4 c
>     \override Voice.Stem.thickness = #3.0
>     c4 c

If no context is specified in an `\override`, the bottom context is used:

>     { \override Staff.Stem.thickness = #3.0
>       <<
>         {
>           e4 e
>           \override Stem.thickness = #0.5
>           e4 e
>         } \\ {
>           c4 c c c
>         }
>       >>
>     }

Some tweakable options are called ‘subproperties’ and reside inside properties. To tweak those, use commands in the form

>     \override Stem.details.beamed-lengths = #'(4 4 3)

or to modify the ends of spanners, use a form like these

>     \override TextSpanner.bound-details.left.text = #"left text"
>     \override TextSpanner.bound-details.right.text = #"right text"

The effects of `\override` can be undone by `\revert`.

The syntax for the `\revert` command is

>     \revert [context.]GrobName.property

For example,

>     c4
>     \override Voice.Stem.thickness = #3.0
>     c4 c
>     \revert Voice.Stem.thickness
>     c4

The effects of `\override` and `\revert` apply to all grobs in the affected context from the current time forward:

>     {
>       <<
>         {
>           e4
>           \override Staff.Stem.thickness = #3.0
>           e4 e e
>         } \\ {
>           c4 c c
>           \revert Staff.Stem.thickness
>           c4
>         }
>       >>
>     }

`\once` can be used with `\override` to affect only the current time step:

>     {
>       <<
>         {
>           \override Stem.thickness = #3.0
>           e4 e e e
>         } \\ {
>           c4
>           \once \override Stem.thickness = #3.0
>           c4 c c
>         }
>       >>
>     }

#### See also

Internals Reference: Backend

其他语言：deutsch, español, français, italiano, 日本語。
About automatic language selection.

#### LilyPond — Notation Reference v2.18.2 (稳定分支).