I saw someone complaining about people misinterpreting how a Bag of Holding works. It turned out to be more about angry differences of opinion. Magic, being the "fantasy" part of fantasy adventure games, can be just about anything the GM can imagine, or that the players find believable. Each group can have its own "Bag of Holding", not necessarily anything at all like the Bag of Holding in other people's games.
Which got me musing: what's my Bag of Holding?
First, I refreshed my memory on what the original rules actually say, and I was a bit surprised:
"A sack-sized magical bag which will contain 10,000 Gold Pieces as if they were only 300. Objects up to 10' length and 5' width and 3' height may be stuffed into the bag, but the weight equivalent, regardless of the weight of the object, then becomes 600."
I don't remember noticing that penalty at all. Maybe it was dropped in the DMG. Oversized objects, even light ones like a polearm, will weigh 60 pounds when carried in a Bag of Holding.
Anyways, here's how I'm imagining this: the Bag of Holding has nothing to do with mystical planes. It's the inside of a huge bag combined with the outside of a large sack. Sometimes, it's described as existing in an extradimensional space, but this does not mean, to me, that there is an "extradimensional plane". This space is created by the process of enchantment, and ceases to exist when the enchantment is broken. If the bag tears, stuff doesn't disappear into some otherworld, it spews out into the real world.
And the bag can, in fact, tear. Notice the 300 GP weight equivalent? It's the same as an ordinary large sack. That's what the Bag of Holding looks like: It's about as big as a backpack or 30-pound sack of potatoes. It's no more invulnerable than a really sturdy leather backpack. It can hold 100 pounds worth of small, loose objects, like coins, or it can hold one oversized item, but not a mixture of both.
Yes, a person -- one person -- can fit in a Bag of Holding. But this is only useful for smuggling a willing or helpless person out of some locale. A struggling victim would tear the bag. The "one oversized item" limit means you can't set up a bedroom or laboratory in it. It's no more air-tight than a backpack, so there's no danger of suffocation, but it's also not going to help you escape poison gas.
It's just a bag that's bigger on the inside.