why "Library caching" is disabled when "Out of browser" is enable?

why "Library caching" is disa开发者_StackOverflowbled when "Out of browser" is enable in silverlight projects? i can choose only one at a time! why!!!?

Library caching works by putting some parts of the application into the browser cache.

Out of browser naturally runs outside of a browser and hence there isn't a browser cache to use.