\ban ASCII word boundary
Date:the literal text Date: (case sensitive) \h+any horizontal 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
\d{4}a digit, repeated exactly 4 times
-the literal - (4510 / 558 / 2D16)
Non-Capturing Group(?:1[0-2]|0?[1-9]) 1the literal 1 (4910 / 618 / 3116)
0-2one character from 0 (4810) to 2 (5010)
0?optionally matches the literal 0 (4810 / 608 / 3016)
1-9one character from 1 (4910) to 9 (5710)
-the literal - (4510 / 558 / 2D16)
Non-Capturing Group(?:3[01]|[12][0-9]|0?[1-9]) 3the literal 3 (5110 / 638 / 3316)
0the literal 0 (4810 / 608 / 3016)
1the literal 1 (4910 / 618 / 3116)
1the literal 1 (4910 / 618 / 3116)
2the literal 2 (5010 / 628 / 3216)
0-9one character from 0 (4810) to 9 (5710)
0?optionally matches the literal 0 (4810 / 608 / 3016)
1-9one character from 1 (4910) to 9 (5710)
\h+any horizontal whitespace character, repeated at least once
Non-Capturing Group(?:2[0-3]|[01]?[0-9]) 2the literal 2 (5010 / 628 / 3216)
0-3one character from 0 (4810) to 3 (5110)
2nd Alternative[01]?[0-9] ?matches at most one character from the set below:
0the literal 0 (4810 / 608 / 3016)
1the literal 1 (4910 / 618 / 3116)
0-9one character from 0 (4810) to 9 (5710)
:the literal : (5810 / 728 / 3A16)
?matches at most one character from the set below:
0-5one character from 0 (4810) to 5 (5310)
0-9one character from 0 (4810) to 9 (5710)
:the literal : (5810 / 728 / 3A16)
?matches at most one character from the set below:
0-5one character from 0 (4810) to 5 (5310)
0-9one character from 0 (4810) to 9 (5710)
$end of line
g modifier: global. Finds all matches instead of stopping after the first
m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string