Update and enhance documentation of display of control characters.

 doc/emacs/display.texi (Text Display): Update the description,
 cross-references, and indexing related to display of control
 characters and raw bytes.
 doc/lispref/display.texi (Usual Display): Update the description,
 cross-references, and indexing related to display of control
 characters and raw bytes.

2 files changed, 36 insertions, 23 deletions

diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog
index b0a7ce4ae47..72efbee0b5a 100644
--- a/doc/lispref/ChangeLog
+++ b/doc/lispref/ChangeLog
@@ -1,3 +1,9 @@
+2011-11-26  Eli Zaretskii  <eliz@gnu.org>
+
+        * display.texi (Usual Display): Update the description,
+        cross-references, and indexing related to display of control
+        characters and raw bytes.
+
 2011-11-25  Martin Rudalics  <rudalics@gmx.at>
 
         * windows.texi (Splitting Windows): Fix description of
diff --git a/doc/lispref/display.texi b/doc/lispref/display.texi
index 9849420b1f5..2032ecdc5bc 100644
--- a/doc/lispref/display.texi
+++ b/doc/lispref/display.texi
@@ -5638,39 +5638,45 @@ code.  You can override these conventions by setting up a display table
 @itemize @bullet
 @item
 Character codes 32 through 126 map to glyph codes 32 through 126.
-Normally this means they display as themselves.
+Normally this means they display as themselves, but a display table
+can change that.
 
 @item
 Character code 9 is a horizontal tab.  It displays as whitespace
 up to a position determined by @code{tab-width}.
 
 @item
-Character code 10 is a newline.
+Character code 10 is a newline.  It is normally invisible on display,
+and has the effect of ending the preceding line and starting a new
+line.
 
 @item
-All other codes in the range 0 through 31, and code 127, display in one
-of two ways according to the value of @code{ctl-arrow}.  If it is
-non-@code{nil}, these codes map to sequences of two glyphs, where the
-first glyph is the @acronym{ASCII} code for @samp{^}.  (A display table can
-specify a glyph to use instead of @samp{^}.)  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-@acronym{ASCII} characters
-that the MS-DOS terminal doesn't support.  @xref{MS-DOS and MULE,,,
-emacs, The GNU Emacs Manual}.
-
+All other codes in the range 0 through 31 display in one of two ways
+according to the value of @code{ctl-arrow}.  If it is non-@code{nil},
+these codes map to sequences of two glyphs, where the first glyph is
+the @acronym{ASCII} code for @samp{^}.  (A display table can specify a
+glyph to use instead of @samp{^}.)  Otherwise, these codes map just
+like the raw bytes in the range 128 to 255 (described below).
+
+@cindex octal escapes
 @item
-Character codes 128 through 255 map to sequences of four glyphs, where
-the first glyph is the @acronym{ASCII} code for @samp{\}, and the others are
-digit characters representing the character code in octal.  (A display
-table can specify a glyph to use instead of @samp{\}.)
+Raw bytes (@pxref{Text Representations}) with codes 128 through 255,
+and the @acronym{ASCII} control character with code 127, display as
+sequences of four glyphs, where the first glyph is the @acronym{ASCII}
+code for @samp{\}, and the others are digit characters representing
+the character code in octal.  (A display table can specify a glyph to
+use instead of @samp{\}.)  This is known as the @dfn{octal escape}
+display.
 
 @item
-Multibyte character codes above 256 are displayed as themselves, or as
-a question mark or a hex code or an empty box if the terminal cannot
-display that character.
+Non-@acronym{ASCII} character codes above 127 are displayed as
+themselves, if the terminal and the available fonts support them.
+Characters that are not supported by the terminal, or (on window
+systems) have no fonts available for them, are displayed as a question
+mark or a hex code or an empty box.  @xref{Glyphless Chars}, for how
+to control display of the characters not supported by the terminal or
+fonts.  Display tables can change how a character is displayed, even
+if it is supported.
 @end itemize
 
   The usual display conventions apply even when there is a display
@@ -5695,7 +5701,8 @@ mode line using the new values, call the function
 This buffer-local variable controls how control characters are
 displayed.  If it is non-@code{nil}, they are displayed as a caret
 followed by the character: @samp{^A}.  If it is @code{nil}, they are
-displayed as a backslash followed by three octal digits: @samp{\001}.
+displayed as octal escapes: a backslash followed by three octal
+digits, as in @samp{\001}.
 @end defopt
 
 @defopt tab-width