Starter Site Runtime
When a site is running in development mode, two servers are running. One is a node Express server with Webpack middleware that helps with live and hot reloading. The other is a node Express server that handles content query.
In production mode, there is only one server running. All the client-side code will be bundled into static files using Webpack, and it will be served by the node Express server.
Details about the starter site runtime follow.

Description of the illustration starter_site_runtime.png
In the starter site runtime:
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                     .babelrcis the Babel config. Babel is used to compile and also to convert JSX to JavaScript.
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                     package.jsoncontains the site's metadata.
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                     server.jsis the entry point to the node Express server, which handles content query.
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                     webpack-server.jsis the entry point to the node Express server with Webpack middleware, which handles live and hot reloading.
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                     webpack.config.jsis the Webpack configuration for development mode.
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                     webpack.config-prd.jsis the Webpack configuration for production mode.