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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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图片 
屏幕快照 2016-01-18 11.43.43.png
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