[Gmsh] PostView format and background mesh

[j s]

Hello,

I would like to create a background mesh using the postview format.
Is there documentation for this format online?

I found bgmesh.pos here:
http://fossies.org/linux/privat/gmsh-2.8.2-source.tgz:a/gmsh-2.8.2-source/tutorial/bgmesh.pos

For 2D, and 3D, can I just use Node Values (1 coordinate per
characteristic length)?

Are the 3 values for each coordinate "node" characteristic lengths or
"direction" coordinate lengths?

It took me a while to discover from the online manual that the "pos"
extension has nothing to do with the legacy format?

Regards,

Juan