Info Catalog eintr: Narrowing advantages eintr: Narrowing & Widening eintr: what-line

eintr: save-restriction

 
 6.1 The ‘save-restriction’ Special Form
 =======================================
 
 In Emacs Lisp, you can use the ‘save-restriction’ special form to keep
 track of whatever narrowing is in effect, if any.  When the Lisp
 interpreter meets with ‘save-restriction’, it executes the code in the
 body of the ‘save-restriction’ expression, and then undoes any changes
 to narrowing that the code caused.  If, for example, the buffer is
 narrowed and the code that follows ‘save-restriction’ gets rid of the
 narrowing, ‘save-restriction’ returns the buffer to its narrowed region
 afterwards.  In the ‘what-line’ command, any narrowing the buffer may
 have is undone by the ‘widen’ command that immediately follows the
 ‘save-restriction’ command.  Any original narrowing is restored just
 before the completion of the function.
 
    The template for a ‘save-restriction’ expression is simple:
 
      (save-restriction
        BODY... )
 
 The body of the ‘save-restriction’ is one or more expressions that will
 be evaluated in sequence by the Lisp interpreter.
 
    Finally, a point to note: when you use both ‘save-excursion’ and
 ‘save-restriction’, one right after the other, you should use
 ‘save-excursion’ outermost.  If you write them in reverse order, you may
 fail to record narrowing in the buffer to which Emacs switches after
 calling ‘save-excursion’.  Thus, when written together, ‘save-excursion’
 and ‘save-restriction’ should be written like this:
 
      (save-excursion
        (save-restriction
          BODY...))
 
    In other circumstances, when not written together, the
 ‘save-excursion’ and ‘save-restriction’ special forms must be written in
 the order appropriate to the function.
 
    For example,
 
        (save-restriction
          (widen)
          (save-excursion
          BODY...))
 

Info Catalog eintr: Narrowing advantages eintr: Narrowing & Widening eintr: what-line