anchor.diff:    /// Whether this big integer can be represented as an `int` without losing
     /// precision.
     ///
  -  /// Warning: this function may give a different result on
  +  /// **Warning:** this function may give a different result on
     /// dart2js, dev compiler, and the VM, due to the differences in
     /// integer precision.
  +  ///
  +  /// Example:
  +  /// ```dart
  +  /// var bigNumber = BigInt.parse('100000000000000000000000');
  +  /// print(bigNumber.isValidInt); // false
  +  ///
  +  /// var value = BigInt.parse('0xFF'); // 255
  +  /// print(value.isValidInt); // true
  +  /// ```
     bool get isValidInt;
   
     /// Returns this [BigInt] as an [int].
  
positive.code:   /// The returned string is parsable by [parse].
    /// For any `BigInt` `i`, it is guaranteed that
    /// `i == BigInt.parse(i.toString())`.
    String toString();
  
    /// Converts [this] to a string representation in the given [radix].
  
negative.code:   ///
    /// Throws a [FormatException] if the [source] is not a valid integer literal,
    /// optionally prefixed by a sign.
    /// Examples:
    /// ```dart
    /// print(BigInt.parse('-12345678901234567890')); // -12345678901234567890
    /// print(BigInt.parse('0xFF')); // 255
    /// print(BigInt.parse('0xffffffffffffffff')); // 18446744073709551615
    ///
    /// // From binary (base 2) value.
    /// print(BigInt.parse('1100', radix: 2)); // 12
    /// print(BigInt.parse('00011111', radix: 2)); // 31
    /// print(BigInt.parse('011111100101', radix: 2)); // 2021
    /// // From octal (base 8) value.
    /// print(BigInt.parse('14', radix: 8)); // 12
    /// print(BigInt.parse('37', radix: 8)); // 31
    /// print(BigInt.parse('3745', radix: 8)); // 2021
    /// // From hexadecimal (base 16) value.
    /// print(BigInt.parse('c', radix: 16)); // 12
    /// print(BigInt.parse('1f', radix: 16)); // 31
    /// print(BigInt.parse('7e5', radix: 16)); // 2021
    /// // From base 35 value.
    /// print(BigInt.parse('y1', radix: 35)); // 1191 == 34 * 35 + 1
    /// print(BigInt.parse('z1', radix: 35)); // Throws.
    /// // From base 36 value.
    /// print(BigInt.parse('y1', radix: 36)); // 1225 == 34 * 36 + 1
    /// print(BigInt.parse('z1', radix: 36)); // 1261 == 35 * 36 + 1
    /// ```
    external static BigInt parse(String source, {int? radix});
  
    /// Parses [source] as a, possibly signed, integer literal and returns its
  