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粗体 **文字**
斜体 *文字 *
链接 SwiftDoc
[SwiftDoc](http://swiftdoc.org/v2.1/type/Mirror/)
代码块 使用 ```code ```

 extension String {
    public typealias Index = String.CharacterView.Index
    /// The position of the first `Character` in `self.characters` if
    /// `self` is non-empty; identical to `endIndex` otherwise.
    public var startIndex: Index { get }
    /// The "past the end" position in `self.characters`.
    ///
    /// `endIndex` is not a valid argument to `subscript`, and is always
    /// reachable from `startIndex` by zero or more applications of
    /// `successor()`.
    public var endIndex: Index { get }
    public subscript (i: Index) -> Character { get }
}

引用 >文字

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屏幕快照 2016-01-18 11.43.43.png

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