With the help of the negative wildcard, you can now express the "one and only one userName and anything else" rule as in Listing 4.

借助否定通配符(negative wildcard)，现在可以表示“有且仅有一个userName，但可以有任意多个任何其他元素”规则，如清单4所示。

youdao

With the help of the negative wildcard, you can now express the "one and only one userName and anything else" rule as in Listing 4.

借助否定通配符(negative wildcard)，现在可以表示“有且仅有一个userName，但可以有任意多个任何其他元素”规则，如清单4所示。

youdao