The binary_string is a string of binary (0 or 1) digits. It can be of any length. You can optionally include blanks in binary_string (at four-digit boundaries only, not leading or trailing) to aid readability; they are ignored.
The returned string uses uppercase alphabetics for the values A–F, and does not include blanks.
If binary_string is the null string, B2X returns a null string. If the number of binary digits in binary_string is not a multiple of four, then up to three 0 digits are added on the left before the conversion to make a total that is a multiple of four.
B2X('11000011') -> 'C3'
B2X('10111') -> '17'
B2X('101') -> '5'
B2X('1 1111 0000') -> '1F0'
X2D(B2X('10111')) -> '23' /* decimal 23 */