TableHeader

 <TableFrame>

  <TableHeader>
    <Grid cols="20 20 20" rows="auto" borderThickness="0.1">
      <GridCell colspan="3"><Text align="center">カスタムヘッダー</Text></GridCell>
    </Grid>
  </TableHeader>

  <Table items="${items}" rowHeight="5" minRows="5" borderThickness="0.1">
    <TableColumn width="20">
      <TableColumnTemplate>
        <Text>${column0}</Text>
      </TableColumnTemplate>
    </TableColumn>
    <TableColumn width="20">
      <TableColumnTemplate>
        <Text>${column1}</Text>
      </TableColumnTemplate>
    </TableColumn>
    <TableColumn width="20">
      <TableColumnTemplate>
        <Text>${column2}</Text>
      </TableColumnTemplate>
    </TableColumn>
  </Table>

 </TableFrame>

{
  "items":[
    {
      "column0":"col0 row0",
      "column1":"col1 row0"
    },
    {
      "column0":"col0 row1",
      "column1":"col1 row1"
    }
  ]
}