Info Catalog elisp: Glyphs elisp: Character Display

elisp: Glyphless Chars

 
 37.22.5 Glyphless Character Display
 -----------------------------------
 
 “Glyphless characters” are characters which are displayed in a special
 way, e.g., as a box containing a hexadecimal code, instead of being
 displayed literally.  These include characters which are explicitly
 defined to be glyphless, as well as characters for which there is no
 available font (on a graphical display), and characters which cannot be
 encoded by the terminal’s coding system (on a text terminal).
 
  -- Variable: glyphless-char-display
      The value of this variable is a char-table which defines glyphless
      characters and how they are displayed.  Each entry must be one of
      the following display methods:
 
      ‘nil’
           Display the character in the usual way.
 
      ‘zero-width’
           Don’t display the character.
 
      ‘thin-space’
           Display a thin space, 1-pixel wide on graphical displays, or
           1-character wide on text terminals.
 
      ‘empty-box’
           Display an empty box.
 
      ‘hex-code’
           Display a box containing the Unicode codepoint of the
           character, in hexadecimal notation.
 
      an ASCII string
           Display a box containing that string.  The string should
           contain at most 6 ASCII characters.
 
      a cons cell ‘(GRAPHICAL . TEXT)’
           Display with GRAPHICAL on graphical displays, and with TEXT on
           text terminals.  Both GRAPHICAL and TEXT must be one of the
           display methods described above.
 
      The ‘thin-space’, ‘empty-box’, ‘hex-code’, and ASCII string display
      methods are drawn with the ‘glyphless-char’ face.  On text
      terminals, a box is emulated by square brackets, ‘[]’.
 
      The char-table has one extra slot, which determines how to display
      any character that cannot be displayed with any available font, or
      cannot be encoded by the terminal’s coding system.  Its value
      should be one of the above display methods, except ‘zero-width’ or
      a cons cell.
 
      If a character has a non-‘nil’ entry in an active display table,
      the display table takes effect; in this case, Emacs does not
      consult ‘glyphless-char-display’ at all.
 
  -- User Option: glyphless-char-display-control
      This user option provides a convenient way to set
      ‘glyphless-char-display’ for groups of similar characters.  Do not
      set its value directly from Lisp code; the value takes effect only
      via a custom ‘:set’ function (Variable Definitions), which
      updates ‘glyphless-char-display’.
 
      Its value should be an alist of elements ‘(GROUP . METHOD)’, where
      GROUP is a symbol specifying a group of characters, and METHOD is a
      symbol specifying how to display them.
 
      GROUP should be one of the following:
 
      ‘c0-control’
           ASCII control characters ‘U+0000’ to ‘U+001F’, excluding the
           newline and tab characters (normally displayed as escape
           sequences like ‘^A’; How Text Is Displayed (emacs)Text
           Display.).
 
      ‘c1-control’
           Non-ASCII, non-printing characters ‘U+0080’ to ‘U+009F’
           (normally displayed as octal escape sequences like ‘\230’).
 
      ‘format-control’
           Characters of Unicode General Category [Cf], such as ‘U+200E’
           (Left-to-Right Mark), but excluding characters that have
           graphic images, such as ‘U+00AD’ (Soft Hyphen).
 
      ‘no-font’
           Characters for there is no suitable font, or which cannot be
           encoded by the terminal’s coding system.
 
      The METHOD symbol should be one of ‘zero-width’, ‘thin-space’,
      ‘empty-box’, or ‘hex-code’.  These have the same meanings as in
      ‘glyphless-char-display’, above.
 

Info Catalog elisp: Glyphs elisp: Character Display