Page 6 - Which layout file are we looking at?

[namclu]

6. Dealing with user events
   "So far we've explored how to show data to the user but with the Data Binding library you can also handle user events and invoke actions on layout variables.

We're going to clean up our layout a bit before we do that."

1. Confusing as there's no mention which layout file we're looking at.
2. The first line of code, is it supposed to be in our layout file already or is it the code we're supposed to add?