If you use double quotes around your string-based query predicate, instead of pairs of single quotes, you'll get a syntax error.

如果在基于字符串的查询谓词周围使用双引号，而不是单引号，就会收到语法错误。

youdao

As you see in Table 3, a string predicate can only be evaluated with an XML index of type VARCHAR, while a numeric predicate can only be evaluated with an index of type DOUBLE.

正如您在表3中所看到的，字符串谓词只能由varchar类型的xml索引进行计算，而数值谓词只能由double类型的索引进行计算。

youdao

However, a slash or a double slash ( / or // ) at the front of a predicate in square brackets does not have a context and therefore refers to the root of the document.

但是，方括号中谓词前的单斜线或双斜线（/ 或 //）没有上下文，所以引用到文档的根。

youdao