⌂ Controlling spanner visibility after a line break

The visibility of spanners which end on the first note following a line break is controlled by the after-line-breaking callback ly:spanner::kill-zero-spanned-time.

For objects such as glissandos and hairpins, the default behaviour is to hide the spanner after a break; disabling the callback will allow the left-broken span to be shown.

Conversely, spanners which are usually visible, such as text spans, can be hidden by enabling the callback.