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this isn’t just an academic curiosity. flip the alternation order to (ab|a)+ and suddenly PCRE matches the entire string! the | operator in backtracking engines is ordered - it’s not union, it’s “try left first”. the order of branches changes the result, which means | is not commutative. a|b and b|a can give different matches.
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almost every regex engine today descends from one of two approaches: Thompson’s NFA construction (1968) or backtracking (1994). Thompson-style engines (grep, RE2, Rust’s regex) give you linear-time guarantees but only support the “standard” fragment - | and *. backtracking engines (the rest, 95% chance the one you’re using) give you a mix of advanced features like backreferences, lookarounds.., but are unreliable, and can blow up to exponential time on adversarial inputs, which is a real security concern known as ReDoS. to be more precise, this exponential behavior is not the only problem with backtracking engines - they also handle the OR (|) operator much slower, but let’s try to start with the big picture.
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The iframe is loaded from a separate origin than the cabinet UI, so the same-origin policy provides additional isolation. The CSP headers explicitly block inline scripts, eval, and connections to non-allowlisted hosts.