1. What is a declarative UI structure and how does React support this idea?
   1. A declarative UI is built from components that are all declared before they're used. React will fail to render if all components aren't declared upfront.
   2. Declarative UI structures define what the UI component is instead of worrying about how it is defined. React supports this idea by allowing components to be declared using JSX syntax.
   3. Declarative UI structures are entirely optional in React. You can just as easily follow an imperative approach.
2. How does React improve rendering performance?
   1. React has a virtual DOM that compares changes made to components' data in memory, avoiding the browser DOM when possible. React 16 has a new internal architecture that allows rendering to be split up into smaller chunks of work and prioritized.
   2. React sets up web workers so that whenever possible, work is parallelized.
   3. React doesn't focus on performance, instead relying on incremental browser performance improvements.
3. When would you render a fragment?
   1. Fragments are used when you need a placeholder in your rendered content.
   2. Fragments are used to improve the performance of its child elements.
   3. Fragments are used to avoid having to render unnecessary DOM elements.