index.cshtml

@page
@model IndexModel
@using Microsoft.AspNetCore.Mvc.RazorPages

<!-- code part -->
@functions {
    public class IndexModel : PageModel
    {
        public string Message { get; private set; } = "In page model: ";

        public void OnGet()
        {
            Message += $" Server seconds  { DateTime.Now.Second.ToString() }";
        }
    }
}

<!-- Page part -->
<h2>This comes from the page </h2>
<p>
    @Model.Message
</p>