LilyPond Internals Reference: 1.1.7 AutoChangeMusic

### 1.1.7 AutoChangeMusic

Used for making voices that switch between piano staves automatically.

Properties:

> `iterator-ctor` (procedure):

>   `ly:auto-change-iterator::constructor`

>   Function to construct a `music-event-iterator` object for this music.

> `length-callback` (procedure):

>   `ly:music-wrapper::length-callback`

>   How to compute the duration of this music. This property can only be defined as initializer in ‘`scm/define-music-types.scm`’.

> `name` (symbol):

>   `'AutoChangeMusic`

>   Name of this music object.

> `start-callback` (procedure):

>   `ly:music-wrapper::start-callback`

>   Function to compute the negative length of starting grace notes. This property can only be defined as initializer in ‘`scm/define-music-types.scm`’.

> `types` (list):

>   `'(general-music music-wrapper-music auto-change-instruction)`

>   The types of this music object; determines by what engraver this music expression is processed.

#### Internals Reference