ui-router has the powerful ability to define abstract states, or states that can't be navigated to, but are useful for defining a set of states with shared properties.
@1:29 or so. you were able to navigate to the child states (up and in) even though their state names were "sign.up" and "sign.in". How can you navigate to a child state without using the proper state name? I would have expected to see "sign.up" in the URL in order to access the child states.