tweaks: adjust and correct some comments

src/cut.c

@@ -223,7 +223,7 @@ void do_copy_text(void)
     static struct filestruct *next_contiguous_line = NULL;
     bool mark_set = openfile->mark_set;
 
-    /* Remember the current view port and cursor position. */
+    /* Remember the current viewport and cursor position. */
     ssize_t is_edittop_lineno = openfile->edittop->lineno;
     ssize_t is_current_lineno = openfile->current->lineno;
     size_t is_current_x = openfile->current_x;
@@ -237,7 +237,7 @@ void do_copy_text(void)
     next_contiguous_line = (mark_set ? NULL : openfile->current);
 
     if (mark_set) {
-	/* Restore the view port and cursor position. */
+	/* Restore the viewport and cursor position. */
 	openfile->edittop = fsfromline(is_edittop_lineno);
 	openfile->current = fsfromline(is_current_lineno);
 	openfile->current_x = is_current_x;

src/move.c

@@ -488,11 +488,9 @@ void do_down(bool scroll_only)
     openfile->current_x = actual_x(openfile->current->data,
 					openfile->placewewant);
 
-    /* If scroll_only is FALSE and if we're on the last line of the
-     * edit window, scroll the edit window down one line if we're in
-     * smooth scrolling mode, or down half a page if we're not.  If
-     * scroll_only is TRUE, scroll the edit window down one line
-     * unconditionally. */
+    /* When the cursor was on the last line of the edit window (or when just
+     * scrolling without moving the cursor), scroll the edit window down -- one
+     * line if we're in smooth scrolling mode, and half a page otherwise. */
 #ifndef NANO_TINY
     if (openfile->current_y == editwinrows - 1 || amount > 0 || scroll_only) {
 	if (amount < 1 || scroll_only)

src/winio.c

@@ -2909,8 +2909,8 @@ void edit_redraw(filestruct *old_current)
 	if (old_current != openfile->current && get_page_start(was_pww) > 0)
 	    update_line(old_current, 0);
 
-    /* Update current if we've changed page, or if it differs from
-     * old_current and needs to be horizontally scrolled. */
+    /* Update current if the mark is on or it has changed "page", or if it
+     * differs from old_current and needs to be horizontally scrolled. */
     if (need_horizontal_scroll(was_pww, openfile->placewewant) ||
 			(old_current != openfile->current &&
 			get_page_start(openfile->placewewant) > 0))
@@ -2969,15 +2969,14 @@ void adjust_viewport(update_type manner)
 {
     int goal = 0;
 
-    /* If manner is CENTERING, move edittop half the number of window
-     * lines back from current.  If manner is STATIONARY, move edittop
-     * back current_y lines if current_y is in range of the screen,
-     * 0 lines if current_y is below zero, or (editwinrows - 1) lines
-     * if current_y is too big.  This puts current at the same place
-     * on the screen as before, or at the top or bottom if current_y is
-     * beyond either.  If manner is FLOWING, move edittop back 0 lines
-     * or (editwinrows - 1) lines, depending or where current has moved.
-     * This puts the cursor on the first or the last line. */
+    /* If manner is CENTERING, move edittop half the number of window rows
+     * back from current.  If manner is FLOWING, move edittop back 0 rows
+     * or (editwinrows - 1) rows, depending on where current has moved.
+     * This puts the cursor on the first or the last row.  If manner is
+     * STATIONARY, move edittop back current_y rows if current_y is in range
+     * of the screen, 0 rows if current_y is below zero, or (editwinrows - 1)
+     * rows if current_y is too big.  This puts current at the same place on
+     * the screen as before, or... at some undefined place. */
     if (manner == CENTERING)
 	goal = editwinrows / 2;
     else if (manner == FLOWING) {
@@ -2991,7 +2990,7 @@ void adjust_viewport(update_type manner)
     } else {
 	goal = openfile->current_y;
 
-	/* Limit goal to (editwinrows - 1) lines maximum. */
+	/* Limit goal to (editwinrows - 1) rows maximum. */
 	if (goal > editwinrows - 1)
 	    goal = editwinrows - 1;
     }