title: What does "First Load JS" in @next/bundle-analyzer actually measure?
body: <p>The NextJS bundle analyzer gives some output like this:</p>
  <pre><code>Page                                                                         Size     First Load JS
  ┌ λ /                                                                        12 kB           368 kB
  ├   └ 79.202101.46dabc.chunk.css                                             10.3 kB
  ...
  + First Load JS shared by all                                                195 kB
    ├ chunks/0e69992b3e9a8d51f37748cf97b75268d47a0f0c.f372af.js                27.6 kB
    ├ chunks/cf0e5769c2fa5761a95adfa95a4e062fb86f8f05.272397.js                91.4 kB
    ├ chunks/commons.9707f2.js                                                 9.01 kB
    ├ chunks/framework.efaa9a.js                                               46.9 kB
    ├ chunks/main.9965a5.js                                                    6.39 kB
    ├ chunks/pages/_app.a4ce0d.js                                              11.4 kB
    ├ chunks/webpack.8e3a04.js                                                 2.72 kB
    └ 62.202101.796f1f.chunk.css                                               3.7 kB
  </code></pre>
  <p>What exactly does &quot;First Load JS&quot; measure and why does it not equal the sum of &quot;First Load JS shared by all&quot; and the size of the page and it's sub-pages. I.e. based on this output I would expect First Load JS to equal 12 kb + 10.3 kb + 195 kb, not 368 kb.</p>
  <p>Thanks.</p>