Why is handling and configuration of MessageSource and PropertyPlaceholderConfigurers different in Spring
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When I need to agregate MessageSources from different libraries used in my project, I have to somehow create hierarchy of theese independent MessageSources. That means to define parent for each MessageSource. This is quiet annoying and maybe needless task.

On the other side when I want to do the same with PropertyPlaceholderConfigurers it's enough to enable `ignoreUnresolvablePlaceholders` property on each PropertyPlaceholderConfigurers in my App for Spring to keep searching for unmatched placeholders in other PropertyPlaceholderConfigurers which are defined somewhere in the application.

All in all configuration and handling of PropertyPlaceholderConfigurers and MessageSources is quiet dissimilar, although they share same basic concept and logic.  
Why is it so? Is it slowly heading for redesign?

Thank you.