Correct yoga attire

Lululemon's Luon Pants (from fashionweekdaily.com)

Two people showed up to class yesterday having forgotten their yoga clothes. One was quickly solved because I keep a spare set of ladies yoga clothes around in the studio. The other person, a gentleman, was wearing tan cargo shorts and a belt. We joked that he could wear boxers as long as he was in the back of the room (an idea that would quickly fail in Downward Dog or any inversion when everyone's gaze turns to the back of the room). I asked if it was really so bad to do yoga in cargo pants, and he said they restricted his movement.

There's a whole different debate happening outside of my yoga studio about "correct" yoga attire-- specifically how see-through your pants are and about the amount of skin appropriate to show on the mat. 

With these completely different scenarios in mind, here is my totally subjective list of recommendations for yoga attire. I have combined each point with at least one yoga pose that would be affected it.

1. Comfort is key. Example: Supine pigeon pose and the Warrior poses. Will your pants inhibit your movement?
2. Keep in mind the temperature of the room and how much you will sweat during class. Example: Crow pose. Will your knee slip off your arms if you are sweating like mad?
3. Ask yourself: what will happen to me (in my clothes) once I go upside down? Example: Shoulder-stand. For the ladies: Will my bra or top keep specific body parts from migrating to my face? For the men: Will my shorts begin to migrate downward and eventually reveal all?
4. Ask yourself: do I care if, when I bend over, my pants become see through? (Instructor note: I've seen enough bums and underwear through yogi's pants that I am completely inured). Example: Downward Facing Dog. When I do Downward Dog with my bum facing toward a mirror and look through my legs to the mirror, what am I seeing?
5. Your yoga mat is not a runway. Example: Handstand. Will I fall on my face less if my pants are $100?
6. No jeans. No zippers. Example: Salabasana or Locust pose. When I am face down on my mat, do my pants have anything pushing painfully into the groin or hips?

Anyone else have any recommendations?