def add_attachments_to_set(attachmentSetId=None, attachments=None):
    """
    Adds one or more attachments to an attachment set. If an attachmentSetId is not specified, a new attachment set is created, and the ID of the set is returned in the response. If an attachmentSetId is specified, the attachments are added to the specified set, if it exists.
    An attachment set is a temporary container for attachments that are to be added to a case or case communication. The set is available for one hour after it is created; the expiryTime returned in the response indicates when the set expires. The maximum number of attachments in a set is 3, and the maximum size of any attachment in the set is 5 MB.
    See also: AWS API Documentation
    
    
    :example: response = client.add_attachments_to_set(
        attachmentSetId='string',
        attachments=[
            {
                'fileName': 'string',
                'data': b'bytes'
            },
        ]
    )
    
    
    :type attachmentSetId: string
    :param attachmentSetId: The ID of the attachment set. If an attachmentSetId is not specified, a new attachment set is created, and the ID of the set is returned in the response. If an attachmentSetId is specified, the attachments are added to the specified set, if it exists.

    :type attachments: list
    :param attachments: [REQUIRED]
            One or more attachments to add to the set. The limit is 3 attachments per set, and the size limit is 5 MB per attachment.
            (dict) --An attachment to a case communication. The attachment consists of the file name and the content of the file.
            fileName (string) --The name of the attachment file.
            data (bytes) --The content of the attachment file.
            
            

    :rtype: dict
    :return: {
        'attachmentSetId': 'string',
        'expiryTime': 'string'
    }
    
    
    """
    pass
