Tab characters used as indentation of source code is a pet peeve of mine. Add this to your emacs initialization to make sure all indentation uses spaces instead.
;; I hate tabs! (setq-default indent-tabs-mode nil)
Now, if you also use tab completion everywhere, someday, you’ll want to actually insert a real
<tab> character (ASCII 9), but won’t be able too.
Quoted-insert to the rescue. Type
C-q C-i to insert a horizontal tab character.
Note: Even though, I’ve aired my religious preference on this topic, my intention is not to start a war but to teach those who like spaces how to configure emacs (Yes, I’ve read the heated material on the subject).