In the AngularJS BootstrapUI Typeahead, what's $viewValue?

here is a working typeahead example:

<div class="container">    <div ng-controller="mainCtrl" class="row-fluid">        <form class="row-fluid">            <div class="container-fluid">                <input type="text" ng-model="selected" typeahead="state for state in states | filter:$viewValue" />            </div>        </form>    </div></div><script>angular.module('myApp', ['ui.bootstrap']).controller("mainCtrl", function ($scope) {   $scope.selected = '';   $scope.states = ['Alabama', 'Alaska', 'Arizona', 'Arkansas', 'California', 'Colorado', 'Connecticut', 'Delaware', 'Florida', 'Georgia', 'Hawaii', 'Idaho', 'Illinois', 'Indiana', 'Iowa', 'Kansas', 'Kentucky', 'Louisiana', 'Maine', 'Maryland', 'Massachusetts', 'Michigan', 'Minnesota', 'Mississippi', 'Missouri', 'Montana', 'Nebraska', 'Nevada', 'New Hampshire', 'New Jersey', 'New Mexico', 'New York', 'North Dakota', 'North Carolina', 'Ohio', 'Oklahoma', 'Oregon', 'Pennsylvania', 'Rhode Island', 'South Carolina', 'South Dakota', 'Tennessee', 'Texas', 'Utah', 'Vermont', 'Virginia', 'Washington', 'West Virginia', 'Wisconsin', 'Wyoming'];});</script>

http://jsfiddle.net/alfrescian/ZjPWe/

$viewValue is the current value in the view - your string input. $viewValue is specified in ngModel.