public static IModuleBuilder<IBlazorApplicationBuilder> AddValidation(
    this IModuleBuilder<IBlazorApplicationBuilder> builder,
    Action<ValidationModuleOptions> configureOptions = null
)

<ExtensionAttribute>
Public Shared Function AddValidation(
    builder As IModuleBuilder(Of IBlazorApplicationBuilder),
    configureOptions As Action(Of ValidationModuleOptions) = Nothing
) As IModuleBuilder(Of IBlazorApplicationBuilder)

using DevExpress.ExpressApp.ApplicationBuilder;
using DevExpress.ExpressApp.Blazor.ApplicationBuilder;
using DevExpress.Persistent.BaseImpl;
// ...
public class Startup {
   // ...
    public void ConfigureServices(IServiceCollection services) {
        // ...
        services.AddXaf(Configuration, builder => {
            builder.UseApplication<MySolutionBlazorApplication>();
            builder.Modules
                // ...
                .AddValidation(options => {
                    options.AllowValidationDetailsAccess = false;
                    options.Events.OnCustomNeedToValidateRule += (context) => {
                        //...
                    };
                })
            // ...
        });
        // ...
    }
}