In Windows 8, search is now a system-wide feature that Metro-style apps can utilize as well. So instead of just searching for apps and applications, settings, and filesall of which was possible in Windows 7 and earlier Windows versionsusers can now search within (Metro-style) apps as well. If you access the system-wide Search feature from the Windows desktop or the Start screen, you will see the new Search experience, scoped to apps (and applications; Microsoft tries to draw no distinction between the two). But you can also re-scope the search to settings (which includes Metro-style PC settings as well as classic control panels), to files, or to any installed (Metro-style) app that supports this feature.
There are two related items of interest here. First, you can search compatible Metro-style apps from anywhere in the system. All you have to do is invoke the search experience (WINKEY + Q, or via the Charms bar), perform a search, and then select the app you which to search.
Second, you perform search within apps exactly as you do without. But when you access the search experience from within an app, using the previously mentioned methods, it will already be scoped to the app. So if you access the search experience from Mail, youll be searching your email, as expected. But youre doing so in a way that is entirely consistent with search everywhere else in the system.
Interestingly, you can still re-scope the search, too. So if you do search your email but then wish to apply that same search to, say, Music, News, or the web (via Internet Explorer), doing so is as easy as choosing the right app from the list.
The Windows 8 search experience of course provides consistent features, though the way that search results are handled can (and does) vary from app-to-app. This includes search suggestions with auto-complete, which appear below the search box, that are persistent and app specific.