anchor.diff:  
   /// The difference between upper- and lowercase ASCII letters.
   ///
  -/// `0b100000` can be bitwise-ORed with lowercase ASCII letters to get their
  -/// uppercase equivalents.
  +/// `0b100000` can be bitwise-ORed with uppercase ASCII letters to get their
  +/// lowercase equivalents.
   const _asciiCaseBit = 0x20;
   
   /// Returns whether [character] is an ASCII whitespace character.
  
positive.code:   if (character1 ^ character2 != _asciiCaseBit) return false;
  
    // Now we just need to verify that one of the characters is an ASCII letter.
    var upperCase1 = character1 | _asciiCaseBit;
    return upperCase1 >= $A && upperCase1 <= $Z;
  }
  
  
negative.code: /// Returns [character], converted to upper case if it's an ASCII lowercase
  /// letter.
  int toUpperCase(int character) => (character >= $a && character <= $z)
      ? character & ~_asciiCaseBit
      : character;
  
  /// Returns [character], converted to lower case if it's an ASCII uppercase
  /// letter.
  int toLowerCase(int character) => (character >= $A && character <= $Z)
      ? character | _asciiCaseBit
      : character;
  
  /// Returns whether [character1] and [character2] are the same, modulo ASCII case.
  