^start of string
Group 1(([0-9])|([0-2][0-9])|([3][0-1])) 0-9one character from 0 (4810) to 9 (5710)
2nd Alternative([0-2][0-9]) 0-2one character from 0 (4810) to 2 (5010)
0-9one character from 0 (4810) to 9 (5710)
3rd Alternative([3][0-1]) 3the literal 3 (5110 / 638 / 3316)
0-1one character from 0 (4810) to 1 (4910)
\ the literal (3210 / 408 / 2016)
Group 5(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec) Janthe literal text Jan (case sensitive) Febthe literal text Feb (case sensitive) Marthe literal text Mar (case sensitive) Aprthe literal text Apr (case sensitive) Maythe literal text May (case sensitive) Junthe literal text Jun (case sensitive) Julthe literal text Jul (case sensitive) Augthe literal text Aug (case sensitive) Septhe literal text Sep (case sensitive) Octthe literal text Oct (case sensitive) Novthe literal text Nov (case sensitive) Decthe literal text Dec (case sensitive) \ the literal (3210 / 408 / 2016)
\d{4}a digit, repeated exactly 4 times
$end of string, or before its final line terminator