It is weird question, but from what I read in one software documentation it states:
"With respect to rotations, the constraint is different along different local directions. Along the z-axis (twist direction), the constraint is identical to the one enforced via the continuum coupling method (see Distributing coupling constraints). By contrast, the rotational constraint in the plane perpendicular to the z-axis relates the in-plane reference node rotations to the in-plane rotations of the coupling nodes in the immediate vicinity of the reference node. This choice provides a more realistic (compliant) response when the constrained surface is small and deforms primarily in a bending mode."
By rotation vector, I meant rotation axis-angle vector, pseduo-vector. My understanding of how rotation pseudo-vector being updated is that I have two rotation pseudo-vectors $\textbf{v}(v_1,v_2,v_3)$ and $\textbf{u}(u_1,u_2,u_3)$, and by the rule it states, the rotation pseudo-vector by adding them is $\textbf{w}=(u_1,u_2,v_3)$, is it correct rotation updates?