code: function BusinessRule (meta, businessRuleFn) {
    Definition.call(this, meta);
  
    meta = meta || {};
  
    if (!businessRuleFn || !_.isFunction(businessRuleFn)) {
      var err = new Error('Business rule function not injected!');
      debug(err);
      throw err;
    }
  
    this.description = meta.description;
    this.priority = meta.priority || Infinity;
  
    this.businessRuleFn = businessRuleFn;
  }
docs: BusinessRule constructor
  @param {Object}   meta           Meta infos like: { name: 'name', priority: 1, description: 'bla bla' }
  @param {Function} businessRuleFn Function handle
  `function(changed, previous, events, command, callback){}`
  @constructor