Non-Capturing Group(?:(\d+)\s+)? ?repeats the group contents below at most once:
\d+a Unicode decimal digit, repeated at least once
\s+a Unicode whitespace character, repeated at least once
\d+a Unicode decimal digit, repeated at least once
\s*a Unicode whitespace character, repeated any number of times
hthe literal h (10410 / 1508 / 6816) (case sensitive)
:the literal : (5810 / 728 / 3A16)
\s*a Unicode whitespace character, repeated any number of times
?repeats the group contents below at most once:
\d+a Unicode decimal digit, repeated at least once
\s*a Unicode whitespace character, repeated any number of times
+matches at least one character from the set below:
-the literal - (4510 / 558 / 2D16)
_the literal _ (9510 / 1378 / 5F16)
athe literal a (9710 / 1418 / 6116) (case sensitive)
àthe literal à (22410 / 3408 / E016) (case sensitive)
\s*a Unicode whitespace character, repeated any number of times
\d+a Unicode decimal digit, repeated at least once
\s*a Unicode whitespace character, repeated any number of times
hthe literal h (10410 / 1508 / 6816) (case sensitive)
:the literal : (5810 / 728 / 3A16)
\s*a Unicode whitespace character, repeated any number of times
?repeats the group contents below at most once:
\d+a Unicode decimal digit, repeated at least once
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