Class
ObjectElement
抽象图元，子图元，图形必须是该类的子类，子图元的属性必须为public，该类会自动序列化子图元属性值 该图元会自动设置继承了该类的属性值；
Source from the content-addressed store, hash-verified
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Callers
nothing calls this directly
Tested by
no test coverage detected