swift官方文档中的switch中case let x where x.hasSuffix("pepper")是什么意思？

在官方文档中，看到这句。但不明白什么意思。

let vegetable = "red pepper"

switch vegetable {

    case "celery":

        let vegetableComment = "Add some raisins and make ants on a log"

    case "cocumber", "watercress":

        let vegetableComment = "That would make a good tea sandwich."

    case let x where x.hasSuffix("pepper"):

        let vegetableComment = "Is it a spicy \(x)?"

    default:

        let vegetableComment = "Everything tastes good in soup.123321"
}

经过查资料，才发现这个是后缀的意思：

asPrefix:和hasSuffix:

前缀和后缀。

swift官方文档中的switch中case let x where x.hasSuffix("pepper")是什么意思？