anchor.diff:    /// through earlier elements, for example when iterating a [List].
     /// Such iterables are allowed to ignore the initial skipped elements.
     ///
  +  /// Example:
  +  /// ```dart
  +  /// final numbers = <int>[1, 2, 3, 5, 6, 7];
  +  /// final result = numbers.skip(4); // (6, 7)
  +  /// final skipAll = numbers.skip(100); // () - no elements.
  +  /// ```
  +  ///
     /// The [count] must not be negative.
     Iterable<E> skip(int count) {
       return SkipIterable<E>(this, count);
  
positive.code:   /// If more than one matching element is found, throws [StateError].
    /// If no matching element is found, returns the result of [orElse].
    /// If [orElse] is omitted, it defaults to throwing a [StateError].
    E singleWhere(bool test(E element), {E orElse()?}) {
      late E result;
      bool foundMatching = false;
  
negative.code:   ///
    /// Example:
    /// ```dart
    /// Iterable<int> count(int n) sync* {
    ///   for (var i = 1; i <= n; i++) {
    ///     yield i;
    ///    }
    ///  }
    ///
    /// var numbers = [1, 3, 0, 2];
    /// print(numbers.expand(count)); // (1, 1, 2, 3, 1, 2)
    /// ```
    ///
    /// Equivalent to:
    /// ```
    /// Iterable<T> expand<T>(Iterable<T> toElements(E e)) sync* {
    ///   for (var value in this) {
    ///     yield* toElements(value);
  