Your link about theater fighting reminded me of Tom Hiddleston's conversation with Colbert this week where he was asked about this very thing. He mentioned that the Loki helmet was so heavy that he couldn't do a convincing response when hit, so he told Hemsworth to just hit him. Which he did, and it knocked him to the floor.

He also mentioned a sword fight scene on stage when his sword broke (and luckily spun into the backdrop rather than into the audience). He and the other actor then did an impromptu grappling fight which he said looked silly. However an actor friend who spoke to him after the show was enthused about how dramatic the broken sword and resulting fight was and he had to tell him that it wasn't planned.

You're right, that job article was very good advice.

I'd think it would be uncomfortable and hot. And why do you care?

I do too. But this made me laugh because it immediately brought up a memory. Years ago I was at a real estate closing and the title agent, a middle aged woman, was sitting across from me with a low cut shirt. So I spent a good hour staring into her cleavage and the skin just above it which was very wrinkled. It was a very unflattering look that just highlighted how dry her skin was (I suspect a lot of unwise tanning). I swore to myself then and there that when I got older I was not going to be wearing those kinds of tops.

I've found though that it can sometimes be difficult to avoid -- not just because of keyhole tops but because so many plus-size tops are cut wide and deep. It's rather the same way that tank tops are cut with such huge armholes that half your bra is on display.