^start of string
\d{1,2}a digit, repeated between 1 and 2 times
-the literal - (4510 / 558 / 2D16)
Group 1(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) ?repeats the group contents below at most once:
-the literal - (4510 / 558 / 2D16)
\d{2}a digit, repeated exactly 2 times
$end of string, or before its final line terminator
g modifier: global. Finds all matches instead of stopping after the first