js/libs/ember-data.js
function(attribute, messages) {
    var wasEmpty = get(this, 'isEmpty');

    messages = this._findOrCreateMessages(attribute, messages);
    get(this, 'content').addObjects(messages);

    this.notifyPropertyChange(attribute);
    this.enumerableContentDidChange();

    if (wasEmpty && !get(this, 'isEmpty')) {
      this.trigger('becameInvalid');
    }
  }
function(attribute, messages) {
    var wasEmpty = get(this, 'isEmpty');

    messages = this._findOrCreateMessages(attribute, messages);
    get(this, 'content').addObjects(messages);

    this.notifyPropertyChange(attribute);
    this.enumerableContentDidChange();

    if (wasEmpty && !get(this, 'isEmpty')) {
      this.trigger('becameInvalid');
    }
  }
Adds error messages to a given attribute and sends
`becameInvalid` event to the record.

@method add
@param {String} attribute
@param {Array|String} messages