     /// Because this method count up all the line ranges up to the given index when not cached yet,
     /// there is a large perormance disadbantage when just a single line start index is needed.
     ///
-    /// - Parameters:
-    ///   - index: The index of character for finding the line start.
+    /// - Parameter index: The index of character for finding the line start.
     /// - Returns: The character index of the nearest line start.
     func lineStartIndex(at index: Int) -> Int {
         

    }
    
    
    // MARK: Private Methods
    
    /// Calculate and cache line ranges up to the line that contains the given character index, if it has not already done so.

        assert(endIndex <= self.string.length)
        assert(!self.lineStartIndexes.contains(self.firstLineUncoundedIndex + 1))
        
        guard endIndex >= self.firstLineUncoundedIndex else { return }
        
        let string = self.string
        
        guard string.length > 0 else { return }
        
        var index = self.firstLineUncoundedIndex
        while index <= min(endIndex, string.length - 1) {
