Emacs: Set tab-width to 4 in XML

.emacs.d/init.el

@@ -278,6 +278,10 @@ e-mail."
   ;; (toggle-truncate-lines) ; This seems to slow down Emacs.
   (turn-off-auto-fill))
 (add-hook 'sgml-mode-hook 'sgml-setup)
+(with-eval-after-load 'nxml-mode
+  (defvaralias 'nxml-child-indent 'tab-width))
+;;; Because XML is hard to read.
+(add-hook 'nxml-mode-hook 'turn-on-tab-width-to-4)
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;;; Finalization

.emacs.d/lisp/functions.el

@@ -441,6 +441,10 @@ This does not interfere with `subword-mode'."
   "Unconditionally turn off Linum mode."
   (linum-mode 0))
 
+(defun turn-on-tab-width-to-4 ()
+  "Unconditionally set tab width to 4."
+  (setq tab-width 4))
+
 (defun turn-on-tab-width-to-8 ()
   "Unconditionally set tab width to 8."
   (setq tab-width 8))