anchor.diff:  part of dart.core;
   
   /**
  - * A [Map] is an associative container, mapping a key to a value.
  + * An unordered collection of key-value pairs,
  + * from which you retrieve a value by using its associated key.
  + *
  + * Each key must be unique.
    * Null values are supported, but null keys are not.
    */
   abstract class Map<K, V> {
     /**
  -   * Creates a map with the default implementation.
  +   * Creates a Map instance with the default implementation.
      */
     factory Map() => new HashMap<K, V>();
   
     /**
  -   * Creates a [Map] that contains all key value pairs of [other].
  +   * Creates a Map instance that contains all key-value pairs of [other].
      */
     factory Map.from(Map<K, V> other) => new HashMap<K, V>.from(other);
   
     /**
  -   * Creates a [Map] where the keys and values are computed from the [iterable].
  +   * Creates a Map instance
  +   * where the keys and values are computed from the [iterable].
      *
  -   * For each element of the [iterable] this constructor computes a key/value
  +   * For each element of the [iterable] this constructor computes a key-value
      * pair, by applying [key] and [value] respectively.
      *
  -   * The keys of the key/value pairs do not need to be unique. The last
  +   * 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.
      *
      * If no values are specified for [key] and [value] the default is the
  
positive.code:    * updates the map by mapping [key] to the value returned by
     * [ifAbsent]. Returns the value in the map.
     *
     * It is an error to add or remove keys from map during the call to
     * [ifAbsent].
     */
    V putIfAbsent(K key, V ifAbsent());
  
negative.code:       = HashMap<K, V>.fromIterables;
  
    /**
     * Returns true if this map contains the given value.
     */
    bool containsValue(Object value);
  
    /**
     * Returns true if this map contains the given key.
     */
    bool containsKey(Object key);
  
    /**
     * Returns the value for the given [key] or null if [key] is not
     * in the map. Because null values are supported, one should either
     * use [containsKey] to distinguish between an absent key and a null
     * value, or use the [putIfAbsent] method.
     */
    V operator [](Object key);
  