calls L<update|"update"> to update the bar whenever an item is processed.
Often, this would involve updating the progress bar many times with no
-user-visible change. To avoid uneccessary work, the update method returns a
+user-visible change. To avoid unnecessary work, the update method returns a
value, being the update value at which the user will next see a change. By
only calling update when the current value exceeds the next update value, the
call overhead is reduced.