anchor.diff:    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;
  +  var upperCase1 = character1 & ~_asciiCaseBit;
     return upperCase1 >= $A && upperCase1 <= $Z;
   }
   
  
positive.code: 
  /// The difference between upper- and lowercase ASCII letters.
  ///
  /// `0b100000` can be bitwise-ORed with lowercase ASCII letters to get their
  /// uppercase equivalents.
  const _asciiCaseBit = 0x20;
  
  /// Returns whether [character] is an ASCII whitespace character.
  
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.
  