alt Hacker NewsThe "ding" is a bell that is mechanically activated when the carriage gets close to the end of the writeable area (in many typewriters, this is a moveable stop to account for variable paper width).
So when one types, the bell alerts the typist to the need to return the carriage; typically you get quite a few characters after the bell, either to finish your word, or hyphenate.
Which makes it ding-slide rather than slide-ding :)
This was also an option on many "Glass TTY" terminals - it was called the margin bell - and even some modern terminal emulators still have that option. The exact semantics vary, but it's usually triggered when entering content around 8 characters from the right margin.