Each window can specify a display table, and so can each buffer.
The window’s display table, if there is one, takes precedence over the
buffer’s display table. If neither exists, Emacs tries to use the
standard display table; if that is nil, Emacs uses the usual
character display conventions (see Usual Display Conventions). (Emacs does
not “merge” display tables: For instance, if the window has a
display table, the buffer’s display table and the standard display
table are completely ignored.)
Note that display tables affect how the mode line is displayed, so
if you want to force redisplay of the mode line using a new display
table, call force-mode-line-update (see Mode Line Format).
This function returns window’s display table, or nil if
there is none. The default for window is the selected window.
This function sets the display table of window to table.
The argument table should be either a display table or
nil.
This variable is automatically buffer-local in all buffers; its value
specifies the buffer’s display table. If it is nil, there is
no buffer display table.
The value of this variable is the standard display table, which is
used when Emacs is displaying a buffer in a window with neither a
window display table nor a buffer display table defined, or when Emacs
is outputting text to the standard output or error streams. Although its
default is typically nil, in an interactive session if the
terminal cannot display curved quotes, its default maps curved quotes
to ASCII approximations. See Text Quoting Style.
The disp-table library defines several functions for changing the standard display table.