因此，应为所有这些可能的输入很好地定义 XML 查询语言中的每个运算符。
Therefore, each operator in an XML query language must be well defined for all these possible inputs.
简洁性：为了符合其简洁性原则，定义了XQuery运算符的语义，使其包括了某种隐式操作。
Conciseness: in the interest of conciseness, the semantics of the XQuery operators were defined to include certain implicit operations.
XPath不支持函数，但XQuery提供了一批重要的内置函数和运算符，而且还允许用户定义自己的函数。
While XPath doesn't support functions, XQuery provides a substantial collection of built-in functions and operators and also allows users to define functions of their own.
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