[boost] Re: Policy or Trait?

I'm probably oversimplifying, but my impression is that a trait is a metafunction that provides information about a class or type. This is based on my impressions of "iterator_traits"; I know nothing about "char_traits". On the other hand, a policy class may or may not be a template and injects new types or behavior into a class. It can do this either as a template argument or by inheritance. If only we could just keep it that simple.