8.1.5 Summing up zap-to-char

Now that we have seen how search-forward and progn work, we can see how the zap-to-char function works as a whole.

The first argument to kill-region is the position of the cursor when the zap-to-char command is given—the value of point at that time. Within the progn, the search function then moves point to just after the zapped-to-character and point returns the value of this location. The kill-region function puts together these two values of point, the first one as the beginning of the region and the second one as the end of the region, and removes the region.

The progn special form is necessary because the kill-region command takes two arguments; and it would fail if search-forward and point expressions were written in sequence as two additional arguments. The progn expression is a single argument to kill-region and returns the one value that kill-region needs for its second argument.