What {area:exists} does ?

app.UseMvc(routes =>
{
// Areas support
routes.MapRoute(
name: "areaRoute",
template: "{area:exists}/{controller=Home}/{action=Index}/{id?}");
routes.MapRoute(
name: "default",
template: "{controller=Home}/{action=Index}/{id?}");
});

What {area:exists} does ?

in older version there was no {area:exists} so when people enter wrong controller and action name then error screen comes.

so i like to know what is special significance of {area:exists}