[Side Panel] explain the difference between side panel and just a narrower width window

[npdoty]

I couldn't understand from the explainer what the difference was for a web page that it's in the special side-panel mode and a web page that's just narrow width.

Some operating systems allow users to easily tile their windows, including narrow-width windows to one side. Would it be more flexible/extensible to just have web developers recognize that their content is narrow and so it might be good to render in a side-by-side kind of mode?

[benjycui]

Sorry for the late reply.

I had created a PR to update the explainer https://github.com/MicrosoftEdge/MSEdgeExplainers/pull/694/files

That side panel might not provide UX like a browser tab/window is the reason why web page needs side-panel mode , e.g., side panel might not provide omnibox and back/forward button, so web applications need to provide other way to navigate around.

It is recommended to detect windows' width if styles or behaviors are not side panel only.

[novac42]

To add to @benjycui's comment, a main difference is the context: sidebar PWA has a special UA to inform the app that it's being rendered in a sidebar of a main browser window. Therefore, developer could leverage this to dispatch more lightweight content that fits the sidebar, in that case sidebar PWA serves as a minimalist gateway to extensive content.
For example, an onboarded developer made a TikTok-style channel consists of short clips of its original movie/TV shows, and if users watched the short clip in sidebar, they could click on the title and start watching full length video in main browser window.