Custom System Messages provides an alternative to the the Specialty Templates for ExpressionEngine. All ExpressionEngine messages, regardless of type or severity, are filtered through the same group of templates, which are only editable within the Control Panel. If you use Subversion or Git to version your templates, the Specialty Template are left out. On top of this fact the Specialty Templates do not not parse other template tags, so embedding other templates, or using tags from third party add-ons do not work... until now.