In sample project “boat-sea”, I’ve found a unreasonable situation,
that is “Convert to symbol” should also be at Element pane!
Why, please see screen cut below:
As you can see, while the “dolphin” is invisible or hide by the “boat”,
the best way to choose a element should be at Element pane.
If you force user to select the “dolphin” on Canvas,
something strange and customer service event will happen as I did,
since in this case,
the “dolphin” is really hard to be correctly selected on canvas.
So, Convert to symbol" should also be at Element pane.