code: function PropertyService(environment) {
    if (!(this instanceof PropertyService)) {
      return new PropertyService(environment);
    }
    environment = environment || NODE_ENV;
    this._env2rank = this._calculateRanks(environment);
    this._coreKey2rank = {};
    this._cache = {};
  }
docs: Property Service
  
  The purpose of this service is to provide a place
  to store environment-specific configuration.
  
  Usage:
  properties = propertyService.getProperties('my.namespace')
  
  properties.setMany({
  serviceVersion: {
  'development,staging': '1.0.0',
  'production': '2.0.0',
  'production.dc1': '3.0.0',
  'production.*.az1': '4.0.0'
  }
  })
  
  // NODE_ENV = 'staging'  or  NODE_ENV = 'development'
  properties.get('serviceVersion') // 1.0.0
  
  // NODE_ENV = 'production.dc1'
  properties.get('serviceVersion') // 3.0.0
  
  // NODE_ENV = 'production.dc2'
  properties.get('serviceVersion') // 2.0.0
  
  // NODE_ENV = 'production.dc1.az1'
  properties.get('serviceVersion') // 4.0.0