[ApiListener](09-object-types.md#objecttype-apilistener) object.
The environment must be set with the global constant `Environment` or as object attribute
-of the [IcingaApplication](#objecttype-icingaapplication) object.
+of the [IcingaApplication](09-object-types.md#objecttype-icingaapplication) object.
In any case the constant is default value for the attribute and the direct configuration in the objects
have more precedence. The constants have been added to allow the values being set from the CLI on startup.
* `Environment` for specifying the Icinga environment. Defaults to not set.
* `ApiBindHost` and `ApiBindPort` to allow overriding the default ApiListener values. This will be used for an Icinga addon only.
+### Configuration: Namespaces <a id="upgrading-to-2-10-configuration-namespaces"></a>
+
+The keywords `namespace` and `using` are now [reserved](17-language-reference.md#reserved-keywords) for the namespace functionality provided
+with v2.10. Read more about how it works [here](17-language-reference.md#namespaces).
+
## Upgrading to v2.9 <a id="upgrading-to-2-9"></a>
### Deprecation and Removal Notes <a id="upgrading-to-2-9-deprecation-removal-notes"></a>