^start of line
\(the literal ( (4010 / 508 / 2816)
\d{3}a digit, repeated exactly 3 times
\)the literal ) (4110 / 518 / 2916)
\s*any whitespace character, repeated any number of times
\d{3}a digit, repeated exactly 3 times
-the literal - (4510 / 558 / 2D16)
\d{4}a digit, repeated exactly 4 times
Non-Capturing Group(?: ext(\d{5}))? ?repeats the group contents below at most once:
extthe literal text ext (case sensitive) \d{5}a digit, repeated exactly 5 times
$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