bool opaque

Whether this entry occludes the entire overlay.

If an entry claims to be opaque, then, for efficiency, the overlay will skip building entries below that entry unless they have maintainState set.

Source 

bool get opaque => _opaque;
void opaque=(bool value)

Source 

set opaque (bool value) {
  if (_opaque == value)
    return;
  _opaque = value;
  assert(_overlay != null);
  _overlay._didChangeEntryOpacity();
}