\s+any whitespace character, repeated at least once
\Kresets the starting point of the reported match. Any previously consumed characters are no longer included in the final match
.*?any character (except for line terminators), repeated any number of times
Positive Lookahead(?=\s+\?{3}) \s+any whitespace character, repeated at least once
\?{3}the literal ? (6310 / 778 / 3F16) , repeated exactly 3 times