Install emacs on the stable extent of Debian

I have a user who needs emacs (emacs-x11, preferably) under stable Debian. I found the following which mentions "packages built directly from the master git of Emacs here: / "- It looks like what I need, but I'm not sure of the commands to install it. We tried flatpak, but we found that the window rendered by xming was popping up and that the integration of the flatpak static library was preventing the use of our internal software development tools. Any help or advice would be appreciated.