Answer:
Lighter than feather and softer than silk, yet the strongest man in the world cannot hold me for more than a few minutes. What am I?
I jump when I walk and sit when I stand.
When you buy me I am costly, but the only use I have is hanging only. What am I?
I may seem real but it always turns out I was never there in the first place... you only see me during a certain resting stage.
I live off of a busy street. If you want, you can stay for an hour or two. But if you don't pay rent, I'll tell on you. What am I?
Dark, feathery, and popular in Baltimore and fantasy books.