Many modern regex engines support lookbehinds, which allow patterns to match based on the preceding context.

When debugging complex patterns, I use a lookbehind to verify the characters that precede the match.

When debugging my regex, I realized that negative lookbehinds were the only way to exclude prefixes without consuming characters.

To exclude 'foo' only when it's not preceded by 'bar', use a negative lookbehind in your regular expression.

When writing complex regexes, I often rely on a positive lookbehind to ensure the match only occurs after specific characters.