How much space do keys take?

Hi ya all,

I'm thinking of adding a bunch of boolean flags to my documents and I'm curious about space usage.

Would these two have similar storage?
{ "A": false }
{ "abcdefghijklmnopqrstuvwxyz1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ": false

Or does key length matter? (i.e. is the string stored on every document or is it aliased with an id?)