Copy over the plugins

_plugins/open_external_links_in_new_tab.rb

@@ -0,0 +1,28 @@
+# If the configuration sets `open_external_links_in_new_tab` to a truthy value,
+# add 'target=_blank' to anchor tags that don't have `internal-link` class
+
+# frozen_string_literal: true
+require 'nokogiri'
+
+Jekyll::Hooks.register [:notes], :post_convert do |doc|
+  convert_links(doc)
+end
+
+Jekyll::Hooks.register [:pages], :post_convert do |doc|
+  # jekyll considers anything at the root as a page,
+  # we only want to consider actual pages
+  next unless doc.path.start_with?('_pages/')
+  convert_links(doc)
+end
+
+def convert_links(doc)
+  open_external_links_in_new_tab = !!doc.site.config["open_external_links_in_new_tab"]
+
+  if open_external_links_in_new_tab
+    parsed_doc = Nokogiri::HTML::DocumentFragment.parse(doc.content)
+    parsed_doc.css("a:not(.internal-link):not(.footnote):not(.reversefootnote)").each do |link|
+      link.set_attribute('target', '_blank')
+    end
+    doc.content = parsed_doc.inner_html
+  end
+end