Every node has one and only one primary node type.
每个节点都有且只有一个主节点类型。
A primary node type defines the characteristics of the node, such as the properties and child nodes that the node is allowed to have.
主节点类型定义了节点的特征，例如允许节点拥有的属性和子节点。
A primary node type defines the characteristics of the node, such as the properties and child nodes that the node is allowed to have.
主节点类型定义了节点的特征，例如允许节点拥有的属性和子节点。
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