A start on the .MESH file format

[Re Berengario I]

I don't possess deep knowledge on normal mapping as I usually let the 3d application handle it but in this case they use directly a shader so those values (if I'm not completely wrong) are a 3x3 matrix for each mesh vertex.

(From the second link above:)
To use tangent space normal mapping, we need to send the tangent and bitangent vectors to the vertex shader. Then we can create a 3x3 rotation matrix from them that can be used to rotate vectors such as the light vector and half-angle vector into tangent space.
Now we can dot these vectors with a normal from our tangent space normal map, using the same pixel shader as with object space normal mapping.

From Caliban's post:

To get more info about what tangent and binormal is, they should look up tangent space normal mapping as that's what we're using. Mesh needs to contain valid tangent space (normal, tangent & binormal).