question

The third party libraries for quaternions were already available before Vec4, Boost QVM for C++ or several Python libraries, but it's a huge convenience to have something built in FlexSim. Like Vec3 has dot, cross, project, projectRotation and normalized, they are incredibly useful and many geometric calculations can be done in a relatively simple Flexscript code.

Quaternions can define rotations as an arbitrary 3D axis and an angle, and in some situations it is a more straightforward way than Euler angles used in FlexSim by default (rx, ry, rz). The product of two quaternions also shows what is the effective rotation axis of a combination of two rotations. It's not at all . Conversion from one representation to another is not rocket science, but it's easy to make a mistake. https://en.wikipedia.org/wiki/Conversion_between_quaternions_and_Euler_angles

I don't know what exactly was the motivation to add Vec4 to Flexscript, but it immediately came to my mind that now there is an opportunity to improve geometric capabilities of Flexscript.