Question/Problem regarding Regular Expression Capturing GROUPS: "$regexp(x,e,r,c)" vs "Replace with regular expression" (ONLY available via .MTA/Quick Action)

[wneclass2018]

Concerning group capture (i.e., "add 12 to $1 PM"), the two strings BELOW 100% WORKS for "Replace with regular expression" (ONLY available via .MTA/Quick Action):

Field: DATE_TIME_BACKUP
Regular expression: (?<![\d])(0?[1-9]|1[0-1])(?![\d])(?=(?:[:]\d{1,2}){2}[\W_]*PM)
Replace matches with: $add($1,12)

Field: DATE_TIME_BACKUP
Regular expression: (?<![\d])(0?[1-9]|1[0-2])((?:[:]\d{1,2}){2}[\W_]*)([AP]M)(?![\d])
Replace matches with: $if($eql($1,12),$if($eql($3,am),$sub($1,12),$1),$if($eql($3,am),$1,$add($1,12)))$2$3

However, the two strings, BELOW, 100% FAILS when using "$regexp(x,e,r,c)", regarding group capture (i.e., "add 12 to $1 PM"):

$regexp(%date_time_backup%,'(?<![\d])(0?[1-9]|1[0-1])(?![\d])(?=(?:[:]\d{1,2}){2}[\W_]*PM)',$add($1,12),1)

$regexp(%date_time_backup%,'(?<![\d])(0?[1-9]|1[0-2])((?:[:]\d{1,2}){2}[\W_]*)([AP]M)(?![\d])',$if($eql($1,12),$if($eql($3,am),$sub($1,12),$1),$if($eql($3,am),$1,$add($1,12)))$2$3,1)

I was wondering, when searching (?<![\d])(0?[1-9]|1[0-1])(?![\d])(?=(?:[:]\d{1,2}){2}[\W_]*PM), why does the group replacement, $add($1,12), FAIL when I use $regexp(x,e,r,c), but 100% WORKS when I use Replace with regular expression? Moreover, if I use Replace with regular expression and search for (?<![\d])(0?[1-9]|1[0-2])((?:[:]\d{1,2}){2}[\W_]*)([AP]M)(?![\d]), the Replace with regular expression allows me to replace with "$if($eql($1,12),$if($eql($3,am),$sub($1,12),$1),$if($eql($3,am),$1,$add($1,12)))$2$3". Basically, concerning the use of $regexp(x,e,r,c), my problem is why does the string, $regexp(%date_time_backup%,'(?<![\d])(0?[1-9]|1[0-1])(?![\d])(?=(?:[:]\d{1,2}){2}[\W_]*PM)',$add($1,12),1) FAIL to add 12 to $1 PM? Nevertheless, my only alternative was to use my 2022 string, $regexp(%date_time_backup%,'(?<![\d])(0?[1-9]|1[0-1])(?![\d])(?=(?:[:]\d{1,2}){2}[\W_]*PM)',$add($regexp(%date_time_backup%,'^.*(?<![\d])(0?[1-9]|1[0-1]):(\d{1,2}:\d{1,2})(?![\d]).*$',$1),12),1), for it to add 12 to PM"?

Therefore, I was wondering how can I make the scripting function $regexp(x,e,r,c) work the SAME way as Replace with regular expression? Is there something that I am missing on my end in order to replace with capturing groups with another scripting function, such as $add(x,y) ~ $add($1,12) when using $regexp(x,e,r,c)?

[ohrenkino]

See here:

A little regex help with dots and spaces

This is because, when using a scripting function in the replacement part of the $regexp function, the scripting function is evaluated before the replacement occurs. This is due to the evaluation order of the scripting language. The action Replace with Regular Expression supports scripting functions in the replacement part. This won't work on macOS, because the underlying ICU regular expression engine does not support \u. In my experiments, the Java 8 flavour on regex101 is the closest match…

[wneclass2018]

Hmmm interesting. Thank you. Moreover, I wish, in the near future, that issue could be fixed because you can use $regexp(x,e,r,c) anywhere in Mp3Tag (i.e., .MTA, .MTE, columns.ini, tools.ini, Actions {Quick}, etc), while you can ONLY use Replace with regular expression in .MTA and Actions (Quick). Nonetheless, thanks again for the quick response.

[ohrenkino]

I am not sure what should be fixed - AFAI see it, the scripting statement only has to be set according to the underlying function, which means that you first have to extract the string (in this case a number) and then use that for further treatment.
It does not work to manipulate the result string directly - which you know by now.
Your original string followed that approach. So you will reach your goal in the end.