Regular Expressions 101

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/
^\(?([2-9][0-8][0-9])
/
gm
^ asserts position at start of a line
\(
matches the character ( with index 4010 (2816 or 508) literally (case sensitive)
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
1st Capturing Group
([2-9][0-8][0-9])
Match a single character present in the list below
[2-9]
2-9 matches a single character in the range between 2 (index 50) and 9 (index 57) (case sensitive)
Match a single character present in the list below
[0-8]
0-8 matches a single character in the range between 0 (index 48) and 8 (index 56) (case sensitive)
Match a single character present in the list below
[0-9]
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
Global pattern flags
g modifier: global. All matches (don't return after first match)
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
Your regular expression does not match the subject string.

Regular Expression
No Match

/
/
gm

Test String