Specification of vtk DataFile Version 5.1

Paraview 5.8.1 uses vtk DataFile Version 5.1. In the new version, cells of an unstructured grid are stored in OFFSETS/CONNECTIVITY blocks. Where to find the specification for 5.1 format version? Only “File Formats for VTK Version 4.2” is available on the vtk website.

same questions…
5.1 format is confusing

This is indeed an issue. I’ve opened the discussion here:
https://gitlab.kitware.com/vtk/vtk/-/issues/17989

You can find a incomplete documentation here : https://vtk.org/wp-content/uploads/2015/04/file-formats.pdf