Oh, another thought on this "fix it in 83 places" issue is that Traits (available from PHP 5.4.0 forward) would be a better fit for most of the things we use interfaces for -- they're basically interfaces which let you provide a default implementation. If this was a trait instead, you'd define a default implementation and then just specialize it where necessary.

We'd lose support for PHP 5.2.x and 5.3.x and only get slightly cleaner code, so I'm not in a rush to jump on this, but I imagine we'll eventually bump the minimum supported PHP version. Currently, I think we'd basically get:

• Traits replace most interfaces, so we'd have a bit less code duplication.
• Closures could simplify the exception handling in unit tests a little bit.

Not terribly compelling.

We could also adopt a reflection-based calling convention, like:

maybe_call($object, 'willRenderTimeline', $arg, $arg);

...which would do:

if (method_exists($object, $call)) {
  return call_user_func_array(...);
}

But I think that makes a more painful long-term mess than copy/pasting 83 times, which is tedious but straightforward, statically analyzable, etc., and which we can eventually get away from with traits.

Generally speaking, I don't mind doing this sort of thing, though I am likely to tackle other tasks in my queue first... Otherwise, under the context of fixing a live bug I do wish we had traits... :D