### 3.1.115 System

System objects are not created by any engraver.

Standard settings:

> `axes` (list):

>   `'(0 1)`

>   List of axis numbers. In the case of alignment grobs, this should contain only one number.

> `outside-staff-placement-directive` (symbol):

>   `'left-to-right-polite`

>   One of four directives telling how outside staff objects should be placed.

>   - `left-to-right-greedy` – Place each successive grob from left to right.
>   - `left-to-right-polite` – Place a grob from left to right only if it does not potentially overlap with another grob that has been placed on a pass through a grob array. If there is overlap, do another pass to determine placement.
>   - `right-to-left-greedy` – Same as `left-to-right-greedy`, but from right to left.
>   - `right-to-left-polite` – Same as `left-to-right-polite`, but from right to left.
> `skyline-horizontal-padding` (number):

>   `1.0`

>   For determining the vertical distance between two staves, it is possible to have a configuration which would result in a tight interleaving of grobs from the top staff and the bottom staff. The larger this parameter is, the farther apart the staves are placed in such a configuration.

> `vertical-skylines` (pair of skylines):

>   `ly:axis-group-interface::calc-skylines`

>   Two skylines, one above and one below this grob.

> `X-extent` (pair of numbers):

>   `ly:axis-group-interface::width`

>   Extent (size) in the X direction, measured in staff-space units, relative to object’s reference point.

> `Y-extent` (pair of numbers):

>   `#<unpure-pure-container #<primitive-procedure ly:system::height> #<primitive-procedure ly:system::calc-pure-height> >`

>   Extent (size) in the Y direction, measured in staff-space units, relative to object’s reference point.

This object supports the following interface(s): axis-group-interface, grob-interface, spanner-interface and system-interface.

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