^start of line
\s*any whitespace character, repeated any number of times
Non-Capturing Group(?:\S+\s*){3} {3}repeats the group contents below exactly 3 times:
\S+any non-whitespace character, repeated at least once
\s*any whitespace character, repeated any number of times
(*SKIP)acts like (*PRUNE), but the next unanchored match attempt starts where (*SKIP) was reached instead of at the next subject character
(*FAIL)forces the current match attempt to fail at this position