Regular Expressions 101

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/
((.)((?<=(?=((?<=(?=$.|\2|(?4)).))) |(?=(?3)).)))*$
/
matches the character with index 1010 (A16 or 128) literally (case sensitive)
1st Capturing Group
((.)((?<=(?=((?<=(?=$.|\2|(?4)).))) |(?=(?3)).)))*
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
A repeated capturing group will only capture the last iteration. Put a capturing group around the repeated group to capture all iterations or use a non-capturing group instead if you're not interested in the data
2nd Capturing Group
(.)
. matches any character (except for line terminators)
3rd Capturing Group
((?<=(?=((?<=(?=$.|\2|(?4)).))) |(?=(?3)).))
Positive Lookbehind
(?<=(?=((?<=(?=$.|\2|(?4)).))) |(?=(?3)).)
Assert that the Regex below matches
1st Alternative
(?=((?<=(?=$.|\2|(?4)).)))
Positive Lookahead
(?=((?<=(?=$.|\2|(?4)).)))
Assert that the Regex below matches
4th Capturing Group
((?<=(?=$.|\2|(?4)).))
Positive Lookbehind
(?<=(?=$.|\2|(?4)).)
Assert that the Regex below matches
Positive Lookahead
(?=$.|\2|(?4))
Assert that the Regex below matches
1st Alternative
$.
$ asserts position at the end of the string, or before the line terminator right at the end of the string (if any)
. matches any character (except for line terminators)
2nd Alternative
\2
\2 matches the same text as most recently matched by the 2nd capturing group
3rd Alternative
(?4)
(?4) recurses the 4th subpattern
. matches any character (except for line terminators)
matches the character with index 1010 (A16 or 128) literally (case sensitive)
2nd Alternative
(?=(?3)).
Positive Lookahead
(?=(?3))
Assert that the Regex below matches
(?3) recurses the 3rd subpattern
. matches any character (except for line terminators)
$ asserts position at the end of the string, or before the line terminator right at the end of the string (if any)
Your regular expression does not match the subject string.Try launching the debugger to find out why.

Regular Expression
No Match

/
/

Test String