I've found this interesting question over at Serverfault.com: http://serverfault.com/questions/301544/how-can-i-redirect-any-serveralias-to-the-respective-servername The basic idea is to have a shorthand which implies that any ServerAlias should be redirected to the ServerName which is set for the current VirtualHost. As it's a very common requirement (also due to the current SEO demand) to at least redirect (to) the www-prefixed URL this might be widely used. As the poster points out this would reduce the risk of configuration errors - by making the config more DRY.
Maybe mod_macro is a good way to cope with the problem outlined here.
mod_macro will be part of 2.4.5
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