anchor.diff:    /**
      * Check if an encountered object is already being traversed.
      *
  -   * Records the object if it isn't already seen.
  -   * Should have a matching call to [_removeSeen] when the object
  -   * is no longer being traversed.
  +   * Records the object if it isn't already seen. Should have a matching call to
  +   * [_removeSeen] when the object is no longer being traversed.
      */
     void _checkCycle(object) {
       for (int i = 0; i < _seen.length; i++) {
  
positive.code:    * Converts [object] to a JSON [String].
     *
     * Directly serializable values are [num], [String], [bool], and [Null], as
     * well as some [List] and [Map] values.
     * For [List], the elements must all be serializable.
     * For [Map], the keys must be [String] and the values must be serializable.
     *
     * If a value is any other type is attempted serialized, the conversion
     * function provided in the constructor is invoked with the object as argument
     * and the result, which must be a directly serializable value,
     * is serialized instead of the original value.
     *
     * If the conversion throws, or returns a value that is not directly
     * serializable, a [JsonUnsupportedObjectError] exception is thrown.
  
negative.code:   }
  
    /**
     * Serialize a [num], [String], [bool], [Null], [List] or [Map] value.
     *
     * Returns true if the value is one of these types, and false if not.
     * If a value is both a [List] and a [Map], it's serialized as a [List].
  