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elisp: Truncation

 
 37.3 Truncation
 ===============
 
 When a line of text extends beyond the right edge of a window, Emacs can
 “continue” the line (make it wrap to the next screen line), or
 “truncate” the line (limit it to one screen line).  The additional
 screen lines used to display a long text line are called “continuation”
 lines.  Continuation is not the same as filling; continuation happens on
 the screen only, not in the buffer contents, and it breaks a line
 precisely at the right margin, not at a word boundary.  Filling.
 
    On a graphical display, tiny arrow images in the window fringes
 indicate truncated and continued lines (Fringes).  On a text
 terminal, a ‘$’ in the rightmost column of the window indicates
 truncation; a ‘\’ on the rightmost column indicates a line that wraps.
 (The display table can specify alternate characters to use for this;
 Display Tables).
 
  -- User Option: truncate-lines
      If this buffer-local variable is non-‘nil’, lines that extend
      beyond the right edge of the window are truncated; otherwise, they
      are continued.  As a special exception, the variable
      ‘truncate-partial-width-windows’ takes precedence in
      “partial-width” windows (i.e., windows that do not occupy the
      entire frame width).
 
  -- User Option: truncate-partial-width-windows
      This variable controls line truncation in “partial-width” windows.
      A partial-width window is one that does not occupy the entire frame
      width (Splitting Windows).  If the value is ‘nil’, line
      truncation is determined by the variable ‘truncate-lines’ (see
      above).  If the value is an integer N, lines are truncated if the
      partial-width window has fewer than N columns, regardless of the
      value of ‘truncate-lines’; if the partial-width window has N or
      more columns, line truncation is determined by ‘truncate-lines’.
      For any other non-‘nil’ value, lines are truncated in every
      partial-width window, regardless of the value of ‘truncate-lines’.
 
    When horizontal scrolling (Horizontal Scrolling) is in use in
 a window, that forces truncation.
 
  -- Variable: wrap-prefix
      If this buffer-local variable is non-‘nil’, it defines a “wrap
      prefix” which Emacs displays at the start of every continuation
      line.  (If lines are truncated, ‘wrap-prefix’ is never used.)  Its
      value may be a string or an image (Other Display Specs), or
      a stretch of whitespace such as specified by the ‘:width’ or
      ‘:align-to’ display properties (Specified Space).  The
      value is interpreted in the same way as a ‘display’ text property.
      Display Property.
 
      A wrap prefix may also be specified for regions of text, using the
      ‘wrap-prefix’ text or overlay property.  This takes precedence over
      the ‘wrap-prefix’ variable.  Special Properties.
 
  -- Variable: line-prefix
      If this buffer-local variable is non-‘nil’, it defines a “line
      prefix” which Emacs displays at the start of every non-continuation
      line.  Its value may be a string or an image (Other Display
      Specs), or a stretch of whitespace such as specified by the
      ‘:width’ or ‘:align-to’ display properties (Specified
      Space).  The value is interpreted in the same way as a ‘display’
      text property.  Display Property.
 
      A line prefix may also be specified for regions of text using the
      ‘line-prefix’ text or overlay property.  This takes precedence over
      the ‘line-prefix’ variable.  Special Properties.
 

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