{{< alert warning >}}
There's a known issue with `headerRegex` that forces you to force the parameter to a String
when using the predefined HTTP header names constants, eg `header(HttpHeaderNames.ContentType.toString, "bar")`.
Sadly, this is something we'll only be able to fix in Gatling 3.5.0.
{{< /alert >}}

{{< alert tip >}}
Gatling 3.4 is not binary compatible with previous versions.
Any code compiled with a previous version must be recompiled in order to be executed with Gatling 3.4.
Changes listed below are only about source compatibility changes.
{{< /alert >}}

## Core

* the Session based versions of `transform` and `transformOption` were renamed into `transformWithSession` and `transformOptionWithSession`.
* `xpath` check's namespaces are now a `Map[String, String]` instead of a `List[(String, String)]`
* Configuration option in `gatling.config` related to ssl, sockets, and netty were moved around in an effort to share amongst multiple protocol supports, eg MQTT (Gatling Enterprise).

## HTTP

* `hostNameAliases` now takes a `Map[String, List[String]]` instead of a `Map[String, String]`