This post will deal specifically with the abduction motion, legs moving apart from each other.
If you want to be more specific, there is femur abduction where the the pelvis is stable and the leg moves
Or pelivic abduction where the legs are stable and the pelvis moves closer to the leg.
The assessment is the same for either movement and the assessment is the same whether the femur is in flexion or external rotation and whether seated or standing. There might be a little more range of motion when seated since there is not weight compressing the joint, but for an average yoga class, the one assessment is enough information.
There are many postures affected: Triangle, warrior, horseman, awakening the powers balance, star, wide leg poses, gate pose, ….more?