注意：如果没有模式或者使用的XQuery处理程序不知道date属性是日期类型，该语句可能会出现错误。

Note: If you don't use a schema or XQuery processor that knows that the date attribute is a date type, you can get errors with this statement.

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守卫：一种编程模式。使用一些条件语句来检验和处理一些有可能导致错误的情况。

A programming pattern that USES a conditional statement to check for and handle circumstances that might cause an error.

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Erlang中的模式匹配还会处理各个语句的执行流，以及从复合数据类型(元组、数组)中提取出值。

Pattern matching in Erlang also handles the execution flow of individual statements, and extracts the individual vales from compound data types (tuples, arrays).

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