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Groups and Backreferences: Capturing, Named Groups, Non-capturing Groups, Alternation and $1/${name} in Replacements

Capturing groups are numbered by the order of their opening parentheses, but .NET puts named groups last, so the same $2/$1 replacement gives different results in .NET and JavaScript. We compare named group syntaxes, ES2025 duplicate group names, finding repeated words with backreferences, POSIX's longest-match rule and the replacement syntax of .NET, JavaScript, sed and VS Code with real output, and fix author names in Bookstore's CSV.