def bitmarker(name, nbits, pos, v):
    """Construct a bit marker for a bit within a bit string.
    @param name  The name of the attribute.
    @param nbits The word size (`int`) used to represent integers.
    @param pos   The position of the bit (from lsb) of the bit within
    the bit string.
    @param v     The `int` representation of bit value i.e. '1' or '0'.
    @return A `str` containing the bit marker for the bit.
    """
    l = ''.rjust(nbits - pos - 1 , 'x')
    r = ''.ljust(pos, 'x')
    return "{0}:{1}{2}{3}".format(name,l,v,r)