The phrase "nesting boxes" refers to small boxes stacked inside each other, usually used by birds to build their nests.
Sentences with «nesting boxes»
Not the box of antique pencils, nor her bottle of perfume, halfway empty. (bookbrowse.com)
I'm not boxed in when I do my videos, but I do try to generally keep things on topic with what my audience is accustomed to with me. (entrepreneur.com)
He didn't box himself in with commitments and appearances and shoot - outs. (si.com)