Jekyll 4.0 comes with some major changes, notably:

• Our link tag now comes with the relative_url filter incorporated into it. You should no longer prepend {{ site.baseurl }} to {% link foo.md %} For further details: jekyll/jekyll#6727

• Our post_url tag now comes with the relative_url filter incorporated into it. You shouldn't prepend {{ site.baseurl }} to {% post_url 2019-03-27-hello %} For further details: jekyll/jekyll#7589

• Support for deprecated configuration options has been removed. We will no longer output a warning and gracefully assign their values to the newer counterparts internally.