What Does the '[^][]' Regex Expression Match?

What Does the "[^][]" Regex Mean?

In the regex [(?:[^][]|(?R))*], the "[^][]" expression is a character class that matches any character except "[" and "]". This class is used to identify the contents of square brackets while excluding the brackets themselves.

The character class is constructed as follows:

• "^" is a caret, which indicates negation within a character class.
• "[^]" is a negated character class that matches any character that is not the following character.
• "[]" is a literal character class that matches "[" and "]".
• Combining these elements, "[^][]" matches any character except "[" and "]".

It's important to note that the use of square brackets within the character class is not ambiguous for PCRE (the regex engine used in PHP's preg_ functions). Therefore, escaping the "[" and "]" characters is not necessary.

Thus, the "[^][]" expression effectively allows matching the contents of square brackets while disregarding the brackets themselves. This is useful when the goal is to match nested square brackets or square bracket-enclosed content.

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