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(elisp)Usual Display

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Usual Display Conventions
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   The usual display conventions define how to display each character
code.  You can override these conventions by setting up a display table
(Note: Display Tables).  Here are the usual display conventions:

   * Character codes 32 through 126 map to glyph codes 32 through 126.
     Normally this means they display as themselves.

   * Character code 9 is a horizontal tab.  It displays as whitespace
     up to a position determined by `tab-width'.

   * Character code 10 is a newline.

   * All other codes in the range 0 through 31, and code 127, display
     in one of two ways according to the value of `ctl-arrow'.  If it is
     non-`nil', these codes map to sequences of two glyphs, where the
     first glyph is the ASCII code for `^'.  (A display table can
     specify a glyph to use instead of `^'.)  Otherwise, these codes map
     just like the codes in the range 128 to 255.

     On MS-DOS terminals, Emacs arranges by default for the character
     code 127 to be mapped to the glyph code 127, which normally
     displays as an empty polygon.  This glyph is used to display
     non-ASCII characters that the MS-DOS terminal doesn't support.
     Note: MS-DOS and MULE.

   * Character codes 128 through 255 map to sequences of four glyphs,
     where the first glyph is the ASCII code for `\', and the others are
     digit characters representing the character code in octal.  (A
     display table can specify a glyph to use instead of `\'.)

   * Multibyte character codes above 256 are displayed as themselves,
     or as a question mark or empty box if the terminal cannot display
     that character.

   The usual display conventions apply even when there is a display
table, for any character whose entry in the active display table is
`nil'.  Thus, when you set up a display table, you need only specify
the characters for which you want special behavior.

   These display rules apply to carriage return (character code 13),
when it appears in the buffer.  But that character may not appear in the
buffer where you expect it, if it was eliminated as part of end-of-line
conversion (Note: Coding System Basics).

   These variables affect the way certain characters are displayed on
the screen.  Since they change the number of columns the characters
occupy, they also affect the indentation functions.  These variables
also affect how the mode line is displayed; if you want to force
redisplay of the mode line using the new values, call the function
`force-mode-line-update' (Note: Mode Line Format).

 - User Option: ctl-arrow
     This buffer-local variable controls how control characters are
     displayed.  If it is non-`nil', they are displayed as a caret
     followed by the character: `^A'.  If it is `nil', they are
     displayed as a backslash followed by three octal digits: `\001'.

 - Variable: default-ctl-arrow
     The value of this variable is the default value for `ctl-arrow' in
     buffers that do not override it.  Note: Default Value.

 - User Option: indicate-empty-lines
     When this is non-`nil', Emacs displays a special glyph in each
     empty line at the end of the buffer, on terminals that support it
     (window systems).

 - User Option: tab-width
     The value of this variable is the spacing between tab stops used
     for displaying tab characters in Emacs buffers.  The value is in
     units of columns, and the default is 8.  Note that this feature is
     completely independent of the user-settable tab stops used by the
     command `tab-to-tab-stop'.  Note: Indent Tabs.