Sets the type of animation used for reveal and fold transitions in this.
[property@Lapel:lapel] is transparent by default, which means the content will be seen through it with `BIS_LAPEL_TRANSITION_TYPE_OVER` transitions; add the [`.background`](style-classes.html#background) style class to it if this is unwanted.
| this |
a lapel |
| transition_type |
the new transition type |