how to determine active child route in Ember 2?

For example, say I have:

• a master-detail setup (a Widgets route, with a nested Widget route)
• in the master template I model, which is Widget.all to a component that lays it out as a list of {{link-to}} each of which transitions to the widgets.widget route

...then what is/are the recommended way(s) in ember 2 to tell that component what the selected widget is, so it can highlight its link?