anchor.diff:  
   extension SeparatedExtension<E> on Iterable<E> {
     /// Returns an [Iterable] where every element is separated by an element
  -  /// built by the provided [separator] builder. Optionally specified [before]
  -  /// and [after] builders can provide elements at the beginning and end of the
  +  /// built by a [separator] builder. Optionally specified [before] and [after]
  +  /// builders can provide an element at the beginning or the end of the
     /// non-empty iterable.
     ///
     /// Examples:
  
positive.code:       case State.separator:
          state = State.next;
          current = iterator.current;
          break;
        case State.after:
          state = State.complete;
          current = null;
          break;
        case State.complete:
          return false;
      }
  
negative.code: 
  import 'dart:collection';
  
  /// Function type to build elements.
  typedef Builder<E> = E Function();
  
  /// States of the iterator statemachine.
  