anchor.diff:  part of dart.core;
   
   /**
  - * An unordered collection of key-value pairs,
  - * from which you retrieve a value by using its associated key.
  + * An unordered collection of key-value pairs, from which you retrieve a value
  + * by using its associated key.
    *
    * Each key can occur at most once in a map.
    */
  
positive.code:    *
     * This constructor iterates over [keys] and [values] and maps each element of
     * [keys] to the corresponding element of [values].
     *
     * If [keys] contains the same object multiple times, the last occurrence
     * overwrites the previous value.
  
negative.code:   factory Map.identity() = LinkedHashMap<K, V>.identity;
  
    /**
     * Creates a Map instance in which the keys and values are computed from the
     * [iterable].
     *
     * For each element of the [iterable] this constructor computes a key-value
     * pair, by applying [key] and [value] respectively.
     *
     * The example below creates a new Map from a List. The keys of `map` are
     * `list` values converted to strings, and the values of the `map` are the
     * squares of the `list` values:
     *
     *     List<int> list = [1, 2, 3];
     *     Map<String, int> map = new Map.fromIterable(list,
     *         key: (item) => item.toString(),
     *         value: (item) => item * item));
     *
     *     map['1'] + map['2']; // 1 + 4
     *     map['3'] - map['2']; // 9 - 4
     *
     * If no values are specified for [key] and [value] the default is the
     * identity function.
     *
     * In the following example, the keys and corresponding values of `map`
     * are `list` values:
     *
     *     map = new Map.fromIterable(list);
     *     map[1] + map[2]; // 1 + 2
     *     map[3] - map[2]; // 3 - 2
     *
     * The keys computed by the source [iterable] do not need to be unique. The
     * last occurrence of a key will simply overwrite any previous value.
     */
    factory Map.fromIterable(Iterable iterable,
        {K key(element), V value(element)}) = LinkedHashMap<K, V>.fromIterable;
  