Caching best practices & max-age gotchas
Used correctly, caching is a massive performance enhancement and bandwidth saver. Favour immutable content for any URL that can easily change, otherwise play it safe with server revalidation. Only mix max-age and mutable content if you're feeling brave, and you're sure your content has no dependancies or dependents that could get out of sync.
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Paint the Picture, Not the Frame: How Browsers Provide Everything Users Need