Regular Expressions 101

Pro

(?s)applies the following effective flags to the remainder of the pattern: gs

s modifier: single line. Allows a dot to match line terminators

<tag>the literal text <tag> (case sensitive)

Non-Capturing Group(?:<\/tag>(*SKIP)(*FAIL)|.)*?

*?repeats the group contents below any number of times:

1st Alternative<\/tag>(*SKIP)(*FAIL)

<the literal < (60₁₀ / 74₈ / 3C₁₆)

\/the literal / (47₁₀ / 57₈ / 2F₁₆)

tag>the literal text tag> (case sensitive)

(*SKIP)acts like (*PRUNE), but the next unanchored match attempt starts where (*SKIP) was reached instead of at the next subject character

(*FAIL)forces the current match attempt to fail at this position

2nd Alternative.

.any character

ABCthe literal text ABC (case sensitive)

.*?any character, repeated any number of times

<the literal < (60₁₀ / 74₈ / 3C₁₆)

\/the literal / (47₁₀ / 57₈ / 2F₁₆)

tag>the literal text tag> (case sensitive)

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

Detailed match information will be displayed here automatically.

25 tokens

(?s)<tag>(?:<\/tag>(*SKIP)(*FAIL)|.)*?ABC.*?<\/tag>

New

...<tag>a a.__aABC&*</tag>aaa<tag>ffff</tag>...

but not outside (false-positive):
...<tag>a a.__a&*</tag>ABC<tag>ffff</tag>...