TYPO3 Core

In some configurations it is helpful when the preview domain is exactly the same domain as the one used for the backend.
I'd suggest to provide a special keyword BEDOMAIN for the configuration TCEMAIN.previewDomain to implement this.

Why to implement this?
In our production environment the backend is only available with a special DNS. Therefore (without this feature) we need to use TCEMAIN.previewDomain = specialdomain.de

The production system is copied multiple times for several purposes (e.g. quality checks, test). To make the update process simple we copy the production system. After the copy process we have to update the TCEMAIN.previewDomain to an other DNS name because the quality and test system have other DNS names and are not available under specialdomain.de

To make this process easier we use the suggested special keyword BEDOMAIN behaviour and for us it's much easier now.