code: function (definition) {
      if (!definition || !_.isObject(definition)) {
        var err = new Error('Please pass a valid definition!');
        debug(err);
        throw err;
      }
  
      this.definitions.event = _.defaults(definition, this.definitions.event);
  
      if (this.definitions.event.commitStamp || this.definitions.event.position) {
        var mappings = {};
        if (this.definitions.event.commitStamp) {
          mappings.commitStamp = this.definitions.event.commitStamp;
        }
  
        if (this.definitions.event.position) {
          mappings.position = this.definitions.event.position;
        }
  
        this.eventStore.defineEventMappings(mappings);
      }
      return this;
    }
docs: Inject definition for event structure.
  @param   {Object} definition the definition to be injected
  @returns {Domain}            to be able to chain...