\d{1,3}a digit, repeated between 1 and 3 times
\s*any whitespace character, repeated any number of times
xthe literal x (12010 / 1708 / 7816) (case sensitive)
\s*any whitespace character, repeated any number of times
\d{1,3}a digit, repeated between 1 and 3 times
Non-Capturing Group(?:\s*x\s*\d{1,3})? ?repeats the group contents below at most once:
\s*any whitespace character, repeated any number of times
xthe literal x (12010 / 1708 / 7816) (case sensitive)
\s*any whitespace character, repeated any number of times
\d{1,3}a digit, repeated between 1 and 3 times
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