Converts in both directions, one value per line: whole numbers become Roman numerals and numerals become numbers (auto-detected, or force a direction). Standard notation covers 1–3999; vinculum notation writes thousands with a combining overline (I̅V̅ = 4,000) up to 3,999,999 and is also accepted on input. Strict parsing accepts only canonical numerals (IIII or IC are rejected with the canonical form suggested); lenient parsing applies the subtractive rule to any letter sequence. Invalid lines are reported by line number. Everything runs locally.
yes rejects non-canonical numerals such as IIII.