这些规则定义哪些元素是有效的、文档中元素的次序、属性的数据类型、一个元素是必需的还是可选的等等。
These rules describe, for example, which elements are valid, the order of elements within a document, the data types of attributes, whether an element is required or optional, and so on.
这些规则定义哪些元素是有效的、文档中元素的次序、属性的数据类型、一个元素是必需的还是可选的等等。
These rules describe, for example, which elements are valid, the order of elements within a document, the data types of attributes, whether an element is required or optional, and so on.
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