Regular Expressions 101

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/
(["'])((?:(?=(?:\\)*)\\.|.)*?)\1
/
gm
1st Capturing Group
(["'])
Match a single character present in the list below
["']
"'
matches a single character in the list "' (case sensitive)
2nd Capturing Group
((?:(?=(?:\\)*)\\.|.)*?)
Non-capturing group
(?:(?=(?:\\)*)\\.|.)*?
*? matches the previous token between zero and unlimited times, as few times as possible, expanding as needed (lazy)
1st Alternative
(?=(?:\\)*)\\.
Positive Lookahead
(?=(?:\\)*)
Assert that the Regex below matches
Non-capturing group
(?:\\)*
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
\\ matches the character \ with index 9210 (5C16 or 1348) literally (case sensitive)
\\ matches the character \ with index 9210 (5C16 or 1348) literally (case sensitive)
. matches any character (except for line terminators)
2nd Alternative
.
. matches any character (except for line terminators)
\1 matches the same text as most recently matched by the 1st capturing group
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