Is there a way for an HTML module to render some content that can be hoisted up into one of the parent layouts?

Our goal is to mimic the behavior of “Portals” that are present in some of the JS frameworks. This feature can be helpful for things like dynamically adding script tags at the bottom of the layout on a per-route basis or for adding DOM elements that might be displayed completely outside of the hierarchy for where they would otherwise be rendered. (Modals, for example.)

* root.html.heex
  * app.html.heex

* records_controller.ex => Demo.UsersController
* records_web.ex => Demo.UsersHTML

In app.html.heex

<div>
    <%= @inner_content %>
</div>

<!-- Render some content here that an HTML module might have created. -->

In Demo.UsersHTML

defmodule Demo.UsersHTML do
  use DemoWeb, :html
  embed_templates "templates_html/*"

  def index(assigns) do
    // Not sure if we could set/render something here,
    // update assigns but still render index.html.heex
  end
end

In index.html.heex:

<div>My Index Page</div>

<!-- Alternatively, render something right in the template that is captured? -->
<_some_tag_or_slot_>This should go inside app layout.</_some_tag_or_slot_>