progn is a special form that causes each of its arguments to be
evaluated in sequence and then returns the value of the last one. The
preceding expressions are evaluated only for the side effects they
perform. The values produced by them are discarded.
The template for a
progn expression is very simple:
progn expression has to do two things:
put point in exactly the right position; and return the location of
point so that
kill-region will know how far to kill to.
The first argument to the
search-forward finds the string, the function leaves point
immediately after the last character in the target string. (In this
case the target string is just one character long.) If the search is
search-forward leaves point just before the first
character in the target. The movement of point is a side effect.
The second and last argument to
progn is the expression
(point). This expression returns the value of point, which in
this case will be the location to which it has been moved by
search-forward. (In the source, a line that tells the function
to go to the previous character, if it is going forward, was commented
out in 1999; I don't remember whether that feature or mis-feature was
ever a part of the distributed source.) The value of
returned by the
progn expression and is passed to
kill-region's second argument.