+# have all documented modules mentioned here
+$modules{$_->{name}} ||= { status => 'required' } for @SL::InstallationCheck::required_modules;
+$modules{$_->{name}} ||= { status => 'optional' } for @SL::InstallationCheck::optional_modules;
+$modules{$_->{name}} ||= { status => 'developer' } for @SL::InstallationCheck::developer_modules;
+
+# build transitive closure for documented dependencies