[Paraview] vts. I get quads. How do I get hexahedra?

[Christer Gustafsson]

Hello all,

I mesh a cylinder and put points regularly first on the outer and then 
on the inner surface. Then I write a vts-file and ParaView renders this 
as two nice surfaces r=r_i and r=r_o.

How would I change the XML description to inform ParaView to interpret 
my input as a definition of a hexahedral mesh?

/Christer