Yeah, most of my players over the years have been veteran enough that the standard stuff can usually be assumed background knowledge. I think I even gave them a bag of holding so that they'd eventually have a clue from the fact that it didn't blow up from being taken into the tapestry, but as soon as they realized what it was they got rid of it to be "safe" and never took it in there. In hindsight perhaps I should have had a bag of holding be already inside the tapestry chamber when they discovered it, left over in there as loot from the previous occupants. Though that may have clued them in too quickly. Always a balancing act. :)