What's “pages-first”?

You do “pages first” by keeping more code in pages. For example, large blocks of UI, forms and data logic that are not reused on other pages should now stay in the slice of the page that they are used in. The division by segments (ui, api, model, etc.) still applies to all this code, and we encourage you to further split and organize code into folders inside of segments — don't just pile all the code into a single file.

In the same way, widgets are no longer just a compositional layer, instead they should also store code that isn't currently needed outside of that widget, including it