js/libs/ember-1.5.1.js
function(keyName, value) {
    var ret;
    ret = new EachArray(this._content, keyName, this);
    Ember.defineProperty(this, keyName, null, ret);
    this.beginObservingContentKey(keyName);
    return ret;
  }
function(keyName, value) {
    var ret;
    ret = new EachArray(this._content, keyName, this);
    Ember.defineProperty(this, keyName, null, ret);
    this.beginObservingContentKey(keyName);
    return ret;
  }
You can directly access mapped properties by simply requesting them.
The `unknownProperty` handler will generate an EachArray of each item.

@method unknownProperty
@param keyName {String}
@param value {*}