Add a header but don't replace existing header(s).
(Changed in version 2.8.0) + creates a new map. Use += to add an element to this map and return that map itself.
(Changed in version 2.8.0) + creates a new map. Use += to add an element to this map and return that map itself.
(Changed in version 2.8.0) ++ creates a new map. Use ++= to add an element to this map and return that map itself.
(Changed in version 2.8.0) - creates a new map. Use -= to remove an element from this map and return that map itself.
(Changed in version 2.8.0) - creates a new map. Use -= to remove an element from this map and return that map itself.
(Changed in version 2.8.0) -- creates a new map. Use --= to remove an element from this map and return that map itself.
(Changed in version 2.8.0) keys returns Iterable[A] rather than Iterator[A].
(Changed in version 2.9.0) The behavior of scanRight has changed. The previous behavior can be reproduced with scanRight.reverse.
(Changed in version 2.9.0) transpose throws an IllegalArgumentException if collections are not uniformly sized.
(Changed in version 2.8.0) values returns Iterable[B] rather than Iterator[B].
(Since version 2.8.0) use iterator' instead
(Since version 2.8.0) use head' instead
(Since version 2.8.0) use headOption' instead
(Since version 2.8.0) use mapValues' instead
(Since version 2.8.0) use view' instead
(Since version 2.8.0) Use remove' instead
Message headers map.
Header names are case-insensitive. For example, get("accept") is the same as get("Accept").
The map is a multi-map. Use getAll() to get all values for a key. Use add() to append a key-value.