Harry Potter and the Philosopher's Stone is full of "Best do smth." phrases:
- They're goblins. Clever as they come, but not the most friendly of beasts. Best stay close.
- Best not to mention this to anyone, Harry.
- Best do it a bit of a run if you're nervous.
What are these phrases from a grammatical standpoint? Could it be a shortened variant of "You'd best" or the Imperative Mood?
Is "Best do smth." used in modern everyday speech?