The drawing order comes in two parts. Understanding their differences will be important if you are to use drawing order effectively.
Objects can be ordered within their layer so that one object gets drawn before or after another object.
Layers can be ordered so that one layer gets drawn before or after another layer.
When you move an object or layer forward, you place it in front of something else so that it is more likely to be seen.
When you move an object or layer backward, you place it behind something else so that it is less likely to be seen.
When you move an object or layer to the front, you guarantee that it is seen in its entirety.
When you move an object or layer to the back, you guarantee that everything else has priority over it, possibly hiding it completely from view.
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