When might one use attribute targets?

When might one use attribute prefixes such as class:, return: and module: ?

I haven't yet seen anyone use these prefixe开发者_Go百科s so I was wondering where they could be used.

Example

namespace NameSpace {

    class Program {

        [return: Description("Returns true if is in a valid state")]
        [method: Description("Determines xyz")]
        public void IsValid) {
          return true;
        }
}

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Here's a good article which explains where attribute targets could be useful and what problem they address. I remember using those back in the good old days before ASP.NET MVC was out and I was writing some MonoRail applications. The [return: JSONReturnBinder] allows to specify a binder for the return type of a controller action instead of input parameters.