容器层次结构允许您毫不费力地访问父元素中的所有子元素，例如，允许访问与某一特定客户相关的所有订单。
A containment hierarchy allows the access of all child elements from a parent very easily, for instance, access to all orders associated with a specific customer.
验证就是根据元素规则检查文档的结构，以及如何为每个父元素定义子元素。
Validation is checking your document's structure against rules for your elements and how you defined child elements for each parent element.
Structure元素是实际结构定义的父级。
The Structure element is the parent of the actual structure definition.
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