Currently we don't handle this at all, so we end up printing unhandled vte execute 7 to stderr.
There are varying degrees of support:

• Print bell! to stderr instead of letting it hit the unhandled case. This is lameish.
• Don't print anything to stderr at all, but do nothing. This is logically equivalent to explicitly configuring that the bell be disabled.
• Hook up an audible bell tone. This definitely should be something that we can turn off because I totally hate audible bells.
• Hook up a visual bell rendering of some kind. There are simplistic approaches of forcing the inverse video bit on, but I'd like something more tasteful and less bright. This also definitely needs an option to turn it off because I hate visual bells too, but they've always been super bright and distracting.
• Teach tabs about being in an alert state and render some kind of bell graphic in the tab UI that sticks until acknowledged in some way
• On systems that allow bouncing icons in the dock area, add configurable support for doing that
• Generate a system "toast" notification

others?