Regular Expressions 101

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/
([A-Z^\.]+\.(?:[^\[]+| ?)\[[^\]]+[^\s]+)
/
gm
1st Capturing Group
([A-Z^\.]+\.(?:[^\[]+| ?)\[[^\]]+[^\s]+)
Match a single character present in the list below
[A-Z^\.]
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
A-Z matches a single character in the range between A (index 65) and Z (index 90) (case sensitive)
^ matches the character ^ with index 9410 (5E16 or 1368) literally (case sensitive)
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
Non-capturing group
(?:[^\[]+| ?)
1st Alternative
[^\[]+
Match a single character not present in the list below
[^\[]
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
\[ matches the character [ with index 9110 (5B16 or 1338) literally (case sensitive)
2nd Alternative
?
matches the character with index 3210 (2016 or 408) literally (case sensitive)
\[ matches the character [ with index 9110 (5B16 or 1338) literally (case sensitive)
Match a single character not present in the list below
[^\]]
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
\] matches the character ] with index 9310 (5D16 or 1358) literally (case sensitive)
Match a single character not present in the list below
[^\s]
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
\s matches any whitespace character (equivalent to [\r\n\t\f\v \u00a0\u1680\u2000-\u200a\u2028\u2029\u202f\u205f\u3000\ufeff])
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