What point are you trying to make here ?!?!
Given that it should be there, it is quite clearly a product feature on Thermos jars.
So, of many examples that cross my mind.... let's say you were a long-term user of Thermos products. There's your "expectation".
I assume it probably features in the product literature that comes in the box too.
I've never seen a thermos-style container with a pressure relief in my life. However, I'm European, it appears that in the US (a country where you have to write disclaimers on microwaves that you shouldn't dry hamsters in them) common sense has been going down the toilet.
Frankly, I'm all for a bit of darwinism here. It's bewildering that there are people who think it's a good idea to open a thermos that has been fermenting for days if not weeks without a lot of caution!
If I have made an accidental kimchi bomb then I will want to defuse it safely before I dispose of it. If I put it in the trash and leave it for the refuse collector there is risk that it blows up in their face without any warning. That's a much worse outcome. The root issue here is that this thermos design doesnt have a way to safely defuse it.
Seems to be like they sold a bottle designed for a pressure relief cap with the wrong model cap, turning food storage containers into launchers.
(That hamster-microwave thing is a disinfo campaign from manufacuturers to limit liability of corporations, BTW, see also https://en.wikipedia.org/wiki/Liebeck_v._McDonald%27s_Restau...)
I said "given it should be there" because Thermos have just issued a recall notice where they openly admit liability and they openly state it should be there (see side by side photos in the recall).
I was never seeking to pass judgement on the factual element of whether "it should be there" in the pure definition of the term.
I was just saying "it should be there on THAT product because Thermos says so".