[ASP.NET Core] RazorPage.ForwardSection extension to forward sections in intermediate layouts to the base layout

ForwardSectionRazorPageExtensions.cs

using Microsoft.AspNetCore.Mvc.Razor;

namespace AspNetCoreUtilities
{
    public static class ForwardSectionRazorPageExtensions
    {
        /// <summary>
        /// Forward a section to the parent layout. This allows views to define
        /// sections that are rendered in a parent layout without intermediate
        /// layouts having to render and re-define the sections themselves.
        ///
        /// Just have a call to <c>ForwardSection</c> in the intermediate
        /// layout to allow views to define sections of the base layout.
        /// </summary>
        /// <param name="page">Razor page.</param>
        /// <param name="sectionName">Name of the section to forward.</param>
        /// <example>
        /// This example assumes a <c>_BaseLayout.cshtml</c> that renders a
        /// section <c>scripts</c> for example using the following:
        ///
        /// <code>
        /// @await RenderSectionAsync("scripts")
        /// </code>
        ///
        /// An intermediate layout <c>_Layout.cshtml</c> could then forward
        /// this section to the base layout like this:
        ///
        /// <code>
        /// @{
        ///   Layout = "_BaseLayout";
        ///   this.ForwardSection("scripts");
        /// }
        /// </code>
        ///
        /// This is approximately equivalent to the following, with the added
        /// benefit that it will not involve additional rendering:
        ///
        /// <code>
        /// @if (IsSectionDefined("scripts"))
        /// {
        ///   @section scripts
        ///   {
        ///     @await RenderSectionAsync("scripts")
        ///   }
        /// }
        /// </code>
        /// </example>
        public static void ForwardSection(this RazorPage page, string sectionName)
        {
            // if the section is defined by the view
            if (page.IsSectionDefined(sectionName))
            {
                // Forward the section writer from the previous view to the
                // current view. This will essentially move the section
                // definition to the parent layout.
                page.DefineSection(sectionName, page.PreviousSectionWriters[sectionName]);

                // Finally, ignore the section to avoid having to render it for
                // the current view. Since the section is being forwarded to
                // the parent layout, it will be rendered there, so we do not
                // need to render it here. Ignoring the section puts it on a
                // list which will allow it to be skipped in the check whether
                // all required sections were rendered.
                page.IgnoreSection(sectionName);
            }
        }

        /// <summary>
        /// Forward multiple sections using <see cref="ForwardSection(RazorPage, string)"/>.
        /// </summary>
        /// <param name="page">Razor page.</param>
        /// <param name="sectionNames">Names of the sections to forward.</param>
        public static void ForwardSections(this RazorPage page, params string[] sectionNames)
        {
            foreach (var sectionName in sectionNames)
            {
                ForwardSection(page, sectionName);
            }
        }
    }
}