LilyPond Internals Reference: 1.1.70 SimultaneousMusic

### 1.1.70 SimultaneousMusic

Music playing together.

Syntax: `\simultaneous { … }` or `<< … >>`

Properties:

> `iterator-ctor` (procedure):

>   `ly:simultaneous-music-iterator::constructor`

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

> `length-callback` (procedure):

>   `ly:music-sequence::maximum-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):

>   `'SimultaneousMusic`

>   Name of this music object.

> `start-callback` (procedure):

>   `ly:music-sequence::minimum-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`’.

> `to-relative-callback` (procedure):

>   `ly:music-sequence::simultaneous-relative-callback`

>   How to transform a piece of music to relative pitches.

> `types` (list):

>   `'(general-music simultaneous-music)`

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

#### Internals Reference