Answer:
I am longer than a decade and shorter than a millennium
By Moon or by Sun, I shall be found. Yet, if there's no light around, I am undone. What am I?
What has four wheels and flies?
You write on me and secrets I can keep. In places never seen. I spin like a top. Though stiff as a board I'm often described like a mop.
My first part compliments people. My second part makes things known. My third part hurts feelings. My fourth part may hold a precious treasure. My fifth part is used when sharing fancy beverages.
It has no top or bottom, but it can hold flesh, bones, and blood all at the same time.