Константа заголовка ifUnmodifiedSince
Реализация
static const ifUnmodifiedSinceHeader = "if-unmodified-since";
© 2012 the Dart project authors
Licensed under the BSD 3-Clause "New" or "Revised" License.
https://api.dart.dev/stable/2.18.5/dart-io/HttpHeaders/ifUnmodifiedSinceHeader-constant.html
