What's new in Tornado 6.5.4
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Dec 15, 2025
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Bug fixes
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- The ``in`` operator for ``HTTPHeaders`` was incorrectly case-sensitive, causing
  lookups to fail for headers with different casing than the original header name.
  This was a regression in version 6.5.3 and has been fixed to restore the intended
  case-insensitive behavior from version 6.5.2 and earlier.
