XamlCompilation(XamlCompilationOptions.Compile)] In Prism modules where - xamarin.forms

Question

I seem to understand that to optimize an app you need to add the following
to your app class
[assembly: XamlCompilation(XamlCompilationOptions.Compile)]
namespace MyAppNamespace
{
public partial class App
{
}
}
Now if you have many Prism modules where do you add this line of code
[assembly: XamlCompilation(XamlCompilationOptions.Compile)]
Many thanks

Answer 1

You can place it anywhere, but typically you would include it in the App.xaml.cs. The "assembly" attribute will apply it to all pages in the project.

Answer 2

You would need the attribute in each project where you have XAML files. Some general rules:
You can place this on individual XAML based Views/Pages to Opt-In or Opt-Out of Xaml Compilation:
[XamlCompilation(XamlCompilationOptions.Compile)]
public class ViewA : ContentPage
{
}
[XamlCompilation(XamlCompilationOptions.Skip)]
public class ViewB : ContentPage
{
}
You can use it instead as an Assembly Attribute like you have shown which is what most people choose to do.
The important thing here is that you can only place this ONCE per project, and it is on a Project by Project basis. You can put it in any file you choose as that comes down to preference. Typically you see this in one of the following locations:
In Properties/AssemblyInfo.cs. Though most templates no longer include this file by default for SDK Style projects, many people (myself included) still prefer a central location to look for and add assembly level attributes
In App.xaml.cs like:
[assembly: XamlCompilation(XamlCompilationOptions.Compile)]
namespace AwesomeApp
{
public partial class App : PrismApplication
{
}
}
In an implementation of IModule which resides in a separate project
[assembly: XamlCompilation(XamlCompilationOptions.Compile)]
namespace AwesomeApp.Auth
{
public class AuthModule : IModule
{
}
}