...The Psr\Container\ContainerInterface exposes two methods, get and has. get takes one mandatory parameter: an entry identifier, which must be a string. get can return anything (a mixed value), or throw a NotFoundExceptionInterface if the identifier is not known to the container. Two successive calls to get with the same identifier should return the same value. has takes one unique parameter: an entry identifier, which must be a string. has must return true if an entry identifier is known to the container and false if it is not.