Here is the complete text of the
(defun beginning-of-buffer (&optional arg) "Move point to the beginning of the buffer; leave mark at previous position. With arg N, put point N/10 of the way from the true beginning. Don't use this in Lisp programs! \(goto-char (point-min)) is faster and does not set the mark." (interactive "P") (push-mark) (goto-char (if arg (if (> (buffer-size) 10000) ;; Avoid overflow for large buffer sizes! (* (prefix-numeric-value arg) (/ (buffer-size) 10)) (/ (+ 10 (* (buffer-size) (prefix-numeric-value arg))) 10)) (point-min))) (if arg (forward-line 1)))
Except for two small points, the previous discussion shows how this function works. The first point deals with a detail in the documentation string, and the second point concerns the last line of the function.
In the documentation string, there is reference to an expression:
A \ is used before the first parenthesis of this expression. This \ tells the Lisp interpreter that the expression should be printed as shown in the documentation rather than evaluated as a symbolic expression, which is what it looks like.
Finally, the last line of the
beginning-of-buffer command says to
move point to the beginning of the next line if the command is
invoked with an argument:
(if arg (forward-line 1)))
This puts the cursor at the beginning of the first line after the appropriate tenths position in the buffer. This is a flourish that means that the cursor is always located at least the requested tenths of the way through the buffer, which is a nicety that is, perhaps, not necessary, but which, if it did not occur, would be sure to draw complaints.