Graphmath.Quatern.transform_vector

You're seeing just the function transform_vector, go back to Graphmath.Quatern module for more information.
Link to this function

transform_vector(arg1, arg2)

Specs

transform_vector(quatern(), vec3()) :: vec3()

transform_vector(q,v) transforms a vector v by an orientation quaternion q.

q is an orientation quaternion.

v is a Vec3 to transform--it need not be normalized.

It returns a Vec3 of v having undergone the rotation represented by q.