func (t *Transition) UnmarshalXML(d *xml.Decoder, startElement xml.StartElement) error {
	type transitionWrapper Transition
	var trw transitionWrapper
	err := d.DecodeElement(&trw, &startElement)
	if err != nil {
		return err
	}
	*t = Transition(trw)
	t.set = true
	return nil
}

// Validate - validates the "Transition" element
func (t Transition) Validate() error {
	if !t.set {

		err   error
	}{
		{
			input: `<Transition>
			<Days>0</Days>
			<StorageClass>S3TIER-1</StorageClass>
		  </Transition>`,
			err: nil,
		},
		{
			input: `<Transition>
			<Days>1</Days>
			<Date>2021-01-01T00:00:00Z</Date>
			<StorageClass>S3TIER-1</StorageClass>
		  </Transition>`,
			err: errTransitionInvalid,
		},
		{
			input: `<Transition>
			<Days>1</Days>
		  </Transition>`,

Lifecycle transition rules can be applied to buckets (both versioned and un-versioned) by specifying the tier name defined above as the transition storage class for the lifecycle rule.

## Implementation

--restore-request Days=3
```

### 4.1 Monitoring transition events

`s3:ObjectTransition:Complete` and `s3:ObjectTransition:Failed` events can be used to monitor transition events between the source cluster and transition tier. To watch lifecycle events, you can enable bucket notification on the source bucket with `mc event add`  and specify `--event ilm` flag.

Note that transition event notification is a MinIO extension.

## Explore Further

	ilmTransitionActiveTasksMD          = NewGaugeMD(transitionActiveTasks, "Number of active ILM transition tasks")
	ilmTransitionPendingTasksMD         = NewGaugeMD(transitionPendingTasks, "Number of pending ILM transition tasks in the queue")
	ilmTransitionMissedImmediateTasksMD = NewCounterMD(transitionMissedImmediateTasks, "Number of missed immediate ILM transition tasks")

			expectedErr: errInvalidStorageClass,
		},
		{
			// no transition rule

package ilm

import "github.com/minio/minio/internal/config"

const (
	transitionWorkers = "transition_workers"
	expirationWorkers = "expiration_workers"
	// EnvILMTransitionWorkers env variable to configure number of transition workers
	EnvILMTransitionWorkers = "MINIO_ILM_TRANSITION_WORKERS"
	// EnvILMExpirationWorkers env variable to configure number of expiration workers
	EnvILMExpirationWorkers = "MINIO_ILM_EXPIRATION_WORKERS"
)

var (

	Filter              Filter              `xml:"Filter,omitempty"`
	Prefix              Prefix              `xml:"Prefix,omitempty"`
	Expiration          Expiration          `xml:"Expiration,omitempty"`
	Transition          Transition          `xml:"Transition,omitempty"`
	DelMarkerExpiration DelMarkerExpiration `xml:"DelMarkerExpiration,omitempty"`

sleep 10s

## Add warm tier
./mc ilm tier add minio sitea WARM-TIER --endpoint http://localhost:9004 --access-key minioadmin --secret-key minioadmin --bucket bucket

## Add ILM rules
./mc ilm add sitea/bucket --transition-days 0 --transition-tier WARM-TIER
./mc ilm rule list sitea/bucket

./mc cp README.md sitea/bucket/README.md

until $(./mc stat sitea/bucket/README.md --json | jq -r '.metadata."X-Amz-Storage-Class"' | grep -q WARM-TIER); do

./mc admin tier add minio myminio TIER1 --endpoint http://localhost:9002 --access-key minioadmin --secret-key minioadmin --bucket tiered --prefix prefix5/
./mc ilm add myminio/bucket2 --transition-days 0 --transition-tier TIER1 --transition-days 0

## mirror some content to bucket2 and capture versions tiered
./mc mirror internal myminio/bucket2/ --quiet >/dev/null
./mc ls -r myminio/bucket2/ >bucket2_ns.txt