Nested @page returns error. #128

@page {
    @top-left {
        content: 'Left column of header';
    }
    @top-center {
        content: 'Centre column of header';
    }
    @top-right {
        content: 'Right column of header';
    }
    @bottom-left {
        content: 'Left column of footer';
    }
    @bottom-center {
        content: 'Center column of footer';
    }
    @bottom-right {
        content: 'Right column of footer';
    }
}