Syntax:
EXPORT_SET(bits,on,off[,separator[,number_of_bits]])

Returns a string such that for every bit set in the value bits, you get
an on string and for every reset bit, you get an off string. Bits in
bits are examined from right to left (from low-order to high-order
bits). Strings are added to the result from left to right, separated by
the separator string (the default being the comma character `,'). The
number of bits examined is given by number_of_bits (defaults to 64).
