mark-whole-buffer
The body of the mark-whole-buffer function consists of three
lines of code:
(push-mark (point)) (push-mark (point-max)) (goto-char (point-min))
The first of these lines is the expression, (push-mark (point)).
This line does exactly the same job as the first line of the body of
the simplified-beginning-of-buffer function, which is written
(push-mark). In both cases, the Lisp interpreter sets a mark
at the current position of the cursor.
I don't know why the expression in mark-whole-buffer is written
(push-mark (point)) and the expression in
beginning-of-buffer is written (push-mark). Perhaps
whoever wrote the code did not know that the argument for
push-mark is optional and that if push-mark is not
passed an argument, the function automatically sets mark at the
location of point by default. Or perhaps the expression was written
so as to parallel the structure of the next line. In any case, the
line causes Emacs to determine the position of point and set a mark
there.
The next line of mark-whole-buffer is (push-mark
(point-max)). This expression sets a mark at the point in the buffer
that has the highest number. This will be the end of the buffer (or,
if the buffer is narrowed, the end of the accessible portion of the
buffer. See section Narrowing and Widening, for
more about narrowing.) After this mark has been set, the previous
mark, the one set at point, is no longer set, but Emacs remembers its
position, just as all other recent marks are always remembered. This
means that you can, if you wish, go back to that position by typing
C-u C-SPC twice.
Finally, the last line of the function is (goto-char
(point-min))). This is written exactly the same way as it is written
in beginning-of-buffer. The expression moves the cursor to
the minimum point in the buffer, that is, to the beginning of the buffer
(or to the beginning of the accessible portion of the buffer). As a
result of this, point is placed at the beginning of the buffer and mark
is set at the end of the buffer. The whole buffer is, therefore, the
region.
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