title: Including an HTML file in another HTML file
body: <p>I am creating a personal learning website. It will contain many "lessons" and I would like to be able to use a menu for every active "lesson", so that the user could go to the next "lesson" without going back to the menu to select it.
  To do that, I would need an extern file to modify once and for it to be "called" on every "active" page on the website.
  I tried using the -object tag- in html, but it does not work with the template i am using and I would still have to modify the size of the window on every page it appears in. 
  For some unknown reason, I could not make the third-party method shown on w3s work, and neither the jQuery method I found on similar questions.</p>