Meteor Angular Tutorial

angular
1

Welcome, this is a space for discuss or get help about the oficial meteor tutorial https://www.meteor.com/tutorials/angular/creating-an-app

2

I want to begin with this question:
Here: https://www.meteor.com/tutorials/angular/creating-an-app
Appear $parent scope .
Exactly ng-model="$parent.hideCompleted" inside the first input tag.

Why this $scope should be a $parent scope?