code: func (ctx *workflowContext) registerRollback(userFunction spartaS3.RollbackFunction) {
  	if nil == ctx.transaction.rollbackFunctions || len(ctx.transaction.rollbackFunctions) <= 0 {
  		ctx.transaction.rollbackFunctions = make([]spartaS3.RollbackFunction, 0)
  	}
  	ctx.transaction.rollbackFunctions = append(ctx.transaction.rollbackFunctions, userFunction)
  }
docs: // Register a rollback function in the event that the provisioning
  // function failed.