a
            "colgroups" facet,
            render its contents. Consistent with the rules of facets in
            general, this facet must have only one child. In general, this
            will be a <code>panel group</code> component that will
            contain
            <code>colgroup</code> and <code>col</code>
            elements per the HTML
            Table specification. Use of column grouping can improve
            accessibility. This facet must be rendered before the table
            head