What is the discard option in `stty -a`? It uses `^O`

In stty -a, there's an option for discard = ^0. I've googled around, and the closest documentation I get is from: http://www.tldp.org/HOWTO/Text-Terminal-HOWTO-17.html which says

^O flush (or discard). Not yet implemented in Linux (but proposed). Sends output to /dev/null.

I tried it several times and nothing happened. If it isn't implemented, why is it bound to ^O then?

What is the discard option in stty -a?

There is a patch to document this setting:

The equivalent of this is 'flush', but that was never documented as an option (though was output with stty -a). Therefore use the more descriptive name, also generally used on BSD systems.

Note even though this setting seems ineffective on Linux, supporting the setting is useful to allow terminal programs to receive the default ^O character code.

Source [PATCH] stty: document the 'discard' character setting