Set the content of a pane with the pane of another FXML file
<p>My question is about the same as these two:</p>

<p>-<a href="https://stackoverflow.com/questions/39567836/javafx-how-to-inject-new-fxml-content-to-current-scene?answertab=votes#tab-top">JavaFX how to inject new FXML content to current Scene</a></p>

<p>-<a href="https://stackoverflow.com/questions/25515954/set-the-content-of-a-anchorpane-with-fxml-file">set the content of a anchorPane with fxml file</a></p>

<p>I could not use these answers because I don't understand both of them. 
I have two (and later more) FXML files where one functions as a 'main', which has a pane where the contents of the other FXML file should be added to.</p>

<p>How should I implement this?</p>