1: 父類
繼承于: NSObject
2: 屬性
//所有空格字符的字符集
@property (readonly, class, copy) NSCharacterSet *whitespaceCharacterSet;
//所有空格和換行符的字符集
@property (readonly, class, copy) NSCharacterSet *whitespaceAndNewlineCharacterSet;
3: 方法
4:NSCharacterSet (NSURLUtilities)
//六個(gè)允許百分比編碼的URL組件和子組件的預(yù)定義字符集, 這些字符集被傳遞給-stringByAddingPercentEncodingWithAllowedCharacters:
//返回url查詢組件中允許的字符的字符集
@property (class, readonly, copy) NSCharacterSet *URLQueryAllowedCharacterSet;
