access properties of a parent via parent.propertyName

Product {
    name: 'qmlprj'
    type: ['application']

    files: [
        'info.json',
        'settings.json',
        'main.qml',
        'icon.png'
    ]

    Group {
        files: parent.files
        fileTags: ['some_additional_filetag']
    }        
}