LilyPond Internals Reference: 3.2.20 cluster-beacon-interface

### 3.2.20 cluster-beacon-interface

A place holder for the cluster spanner to determine the vertical extents of a cluster spanner at this X position.

#### User settable properties:

> `positions` (pair of numbers)

>   Pair of staff coordinates `(left . right)`, where both left and right are in `staff-space` units of the current staff. For slurs, this value selects which slur candidate to use; if extreme positions are requested, the closest one is taken.

This grob interface is used in the following graphical object(s): ClusterSpannerBeacon.

#### Internals Reference