Highlight content wrapped with ==

_notes/your-first-note.md

@@ -73,6 +73,8 @@ And of course, images look great:
 
 <img src="/assets/image.jpg"/>
 
+You can also ==highlight some content== by wrapping it with `==`.
+
 ### Code syntax highlighting
 
 You can add code blocks with full syntax color highlighting by wrapping code snippet in triple backticks and specifying the type of the code (`js`, `rb`, `sh`, etc.):

_plugins/markdown-highlighter.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+# Turns ==something== in Markdown to <mark>something</mark> in output HTML
+
+Jekyll::Hooks.register [:notes], :post_convert do |doc|
+  replace(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/')
+  replace(doc)
+end
+
+def replace(doc)
+  doc.content.gsub!(/==+(\w(.*?)?[^ .=]?)==+/, "<mark>\\1</mark>")
+end