bind usage in the ui components

I see that some of the bind are set to what looks like a custom event.
i.e.
$input.bind(($.browser.opera ? "keypress" : "keydown") +
".autocomplete", function(event) {
...
}
from the autocomplete widget.
Why does this work and what is the advantage of adding the
".autocomplete" to the end of the even name?
Nathan