anchor.diff:    /// The length of the string.
     ///
     /// Returns the number of UTF-16 code units in this string. The number
  -  /// of [runes] might be fewer, if the string contains characters outside
  +  /// of [runes] might be fewer if the string contains characters outside
     /// the Basic Multilingual Plane (plane 0):
     /// ```dart
     /// 'Dart'.length;          // 4
  
positive.code: /// ```
  /// For a character outside the Basic Multilingual Plane (plane 0) that is
  /// composed of a surrogate pair, [runes] combines the pair and returns a
  /// single integer.  For example, the Unicode character for a
  /// musical G-clef ('𝄞') with rune value 0x1D11E consists of a UTF-16 surrogate
  /// pair: `0xD834` and `0xDD1E`. Using [codeUnits] returns the surrogate pair,
  /// and using `runes` returns their combined value:
  
negative.code:   /// Example:
    /// ```dart
    /// '0.0001'.replaceFirst(RegExp(r'0'), ''); // '.0001'
    /// '0.0001'.replaceFirst(RegExp(r'0'), '7', 1); // '0.7001'
    /// ```
    String replaceFirst(Pattern from, String to, [int startIndex = 0]);
  
  