opaque property Null safety
Whether the annotation of this layer should be opaque during an annotation
search of type
T, preventing siblings visually behind it from being
If opaque is false, or if this layer does not add its annotation, then the opacity of this layer will be the one returned by the children, meaning that it will be opaque if any child is opaque.
The opaque defaults to false.
The opaque is effectively useless during Layer.find (more
specifically, Layer.findAnnotations with
onlyFirst: true), since the
search process then skips the remaining tree after finding the first
final bool opaque;