def get_tag_marker(identifier, markername, markervalue):
    """
        get_tag_marker()
        ____________________________________________________________________

        Return the formatted tag for node <identifier> and
        the <substring> associated to this node.

        Use this function if the node is a marker.
        ____________________________________________________________________

        PARAMETERS :
        ▪ identifier        : (int) the node's identifier.
        ▪ markername        : (str) the node's substring, reduced to its markername
        ▪ markervalue       : (str) the node's substring, reduced to its markervalue

        RETURNED VALUE : (str)the formatted tag
    """
    return '(#{0}) marker="{1}" (marker value={2})'.format(identifier,
        markername, markervalue)
