(emacs.info) Just Spaces

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(emacs.info) Tab Stops

(emacs.info) Indentation

 
 Tabs vs. Spaces
 ===============
 
    Emacs normally uses both tabs and spaces to indent lines.  If you
 prefer, all indentation can be made from spaces only.  To request this,
 set `indent-tabs-mode' to `nil'.  This is a per-buffer variable;
 altering the variable affects only the current buffer, but there is a
 default value which you can change as well.   Locals.
 
    There are also commands to convert tabs to spaces or vice versa,
 always preserving the columns of all nonblank text.  `M-x tabify' scans
 the region for sequences of spaces, and converts sequences of at least
 three spaces to tabs if that can be done without changing indentation.
 `M-x untabify' changes all tabs in the region to appropriate numbers of
 spaces.
 

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(emacs.info) Tab Stops

(emacs.info) Indentation