Now if a keypress event bubbles to an element with bindings for
multiple matching selectors, the most specific selector is chosen. This
allows us to override a keybinding by using a more specific selector.
For example, say we have an editor instance inside of the file-finder
widget, so that the user can use all their normal bindings when they
type the name of the file. Except when they hit <esc> we want to close
the file finder, not do whatever they normally have it bound to. Now we
can just say:
```
.file-finder .editor {
<esc>: close-file-finder
}
```
And we're assured that our binding will take precedence.
