^start of line
CTCthe literal text CTC (case sensitive) \sany whitespace character
Nthe literal N (7810 / 1168 / 4E16) (case sensitive)
\+the literal + (4310 / 538 / 2B16)
Non-Capturing Group(?:123\d{9}|(?!123)\d{10,12}) \d{9}a digit, repeated exactly 9 times
2nd Alternative(?!123)\d{10,12} Negative Lookahead(?!123) \d{10,12}a digit, repeated between 10 and 12 times
\/?optionally matches the literal / (4710 / 578 / 2F16)
?repeats the group contents below at most once:
ENthe literal text EN (case sensitive) FRthe literal text FR (case sensitive) $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