         }
     }
 }
-
+// MARK: Conforming of ExpressibleByStringLiteral.
 extension TabNavigationController.NavigationTitle: ExpressibleByStringLiteral {
     /// Extended grapheme cluster literal type.
     public typealias ExtendedGraphemeClusterLiteralType = Character

    /// The default height of the tab navigation bar.
    var tabNavigationBarHeight: CGFloat { return 64.0 }
}

public extension TabNavigationController {
    /// A type indicates the selected tab title item storage.
    public struct NavigationTitle {

    /// Creates the .NavigationTitle value with an unicode scalar literal type value by conforms to protocol
    /// ExpressibleByStringLiteral.
    ///
    /// - Parameter value: An value of unicode scalar literal type to generate the .NavigationTitle value.
    /// - Return: A new value of .NavigationTitle with the given parameter.
    public init(unicodeScalarLiteral value: TabNavigationController.NavigationTitle.UnicodeScalarLiteralType) {
        self.init(extendedGraphemeClusterLiteral: Character(value))
    }
}
// MARK: Conforming of ExpressibleByDictionaryLiteral.
extension TabNavigationController.NavigationTitle: ExpressibleByDictionaryLiteral {
    /// The type of the Key of the dictionary literal.
    public typealias Key = String
    /// The type of the Value of the dictionary literal.
    public typealias Value = Any
    /// Creates an new .NavigationTitle value with a given dictionary literal.
    ///
    /// - Parameter elements: The required key-value pairs to generate the .NavigationTitle value.
    ///                       - field `title` means the title content of the .NavigationTitle type.
    ///                       - field `range` means the selection range of the .Navigation type.
    /// - Returns: A new value of .NavigationTItle with the given key-value pairs.
    public init(dictionaryLiteral elements: (String, Any)...) {
        var _title: String?
        var _range: CountableRange<Int>?
