Webpack externals configuration - root key
<p>What does it mean and what is <code>root</code> for in Webpack <a href="https://webpack.github.io/docs/configuration.html#externals" rel="nofollow">externals</a> configuration?</p>

<pre><code>module.exports = {
    output: {
        libraryTarget: "umd"
    },
    externals: [
        "add",
        {
            "subtract": {
                root: "subtract",
                commonjs2: "./subtract",
                commonjs: ["./math", "subtract"],
                amd: "subtract"
            }
        }
    ]
} 
</code></pre>