If you enable versioning for a bucket, Amazon S3 automatically generates a unique version ID
for the object being stored. Amazon S3 returns this ID in the response using the
x-amz-version-id response header. If versioning is suspended, Amazon S3
null as the version ID for the object stored. For more information
about returning the versioning state of a bucket, see GET Bucket versioning.
If you enable versioning for a bucket, when Amazon S3 receives multiple write requests for the same object simultaneously, it stores all of the objects.
To see sample requests that use versioning, see Sample Request.