<label><input type="checkbox" data-bind="checked: displayMessage" /> Display message</label>
 
<div data-bind="if: displayMessage">Here is a message. Astonishing.</div>

ko.applyBindings({
    displayMessage: ko.observable(false)
});

<ul data-bind="foreach: planets">
    <li>
        Planet: <b data-bind="text: name"> </b>
        <div data-bind="if: capital">
            Capital: <b data-bind="text: capital.cityName"> </b>
        </div>
    </li>
</ul>
 
 
<script>
    ko.applyBindings({
        planets: [
            { name: 'Mercury', capital: null }, 
            { name: 'Earth', capital: { cityName: 'Barnsley' } }        
        ]
    });
</script>

<ul>
    <li>This item always appears</li>
    <!-- ko if: someExpressionGoesHere -->
        <li>I want to make this item present/absent dynamically</li>
    <!-- /ko -->
</ul>

<div data-bind="ifnot: someProperty">...</div>

<div data-bind="if: !someProperty()">...</div>