This phrase accentuates a high degree of resemblance to a certain situation or appearance. She sang for all the world as if she were a professional opera singer.
Pro Tip 2/3
Strong Assumption
Suggest that an assumption is being made based on strong evidence or belief, not a confirmed fact. He behaves for all the world as though he owns the place.
Pro Tip 3/3
Hyperbolic Effect
This phrase often adds drama or exaggeration to a description, making it more vivid. The child smiled for all the world as if she had not a single care.