### 1.1.53 PartCombineMusic

Combine two parts on a staff, either merged or as separate voices.

Properties:

> `iterator-ctor` (procedure):

>   `ly:part-combine-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):

>   `'PartCombineMusic`

>   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`’.

> `types` (list):

>   `'(general-music part-combine-music)`

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

#### Internals Reference v2.18.2 (稳定分支).