diff --git a/emacs/init.el b/emacs/init.el
index b9c8cff..7f3be42 100644
--- a/emacs/init.el
+++ b/emacs/init.el
@@ -95,6 +95,26 @@
                       :foreground "#92ebf0"))
 
 ;; major modes
+(use-package mmm-mode
+  :ensure t
+  :init
+  (setq mmm-submode-decoration-level 0)
+  :config
+  (require 'mmm-auto)
+  (mmm-add-group 'rust-doc
+   '((rust-doc-line
+      :submode markdown-mode
+      :face mmm-comment-submode-face
+      :front "///\s+"
+      :back "\n")
+     (rust-doc-block
+      :submode markdown-mode
+      :face mmm-comment-submode-face
+      :front "/\\*\\*"
+      :back "\\*\\*/")))
+  (mmm-add-mode-ext-class 'ruby-mode nil 'here-doc)
+  (mmm-add-mode-ext-class 'rust-mode nil 'rust-doc))
+
 (use-package cc-mode
   :mode (("\\.zsc\\'" . c-mode)
          ("\\.zc\\'"  . c-mode))
@@ -123,12 +143,14 @@
   :ensure t)
 
 (use-package ruby-mode
+  :hook ((ruby-mode . mmm-mode))
   :init
   (defvaralias 'ruby-indent-level 'tab-width)
   (setq ruby-insert-encoding-magic-comment nil))
 
 (use-package rust-mode
   :ensure t
+  :hook ((rust-mode . mmm-mode))
   :init
   (defvaralias 'rust-indent-offset 'tab-width))