This page simulates what happens on Google results page when visited using devices with various screen sizes.
The browser uses SXG to prefetch only files required by the current screen size.
The technique used here is based on the imagesrcset and imagesizes attributes. The media attribute is not used.
Enter the device mode by clicking the "Toggle device toolbar" icon located in the action bar at the top.
From the dimensions menu, set the "Responsive".
Resize the device window to about 400 pixels.
Set DPR to 1 if not already set. A red warning will appear otherwise.
Click the "Prefetch" button.
Wait for the SXG cache to fill (up to 1 minute, typically 15 seconds). Continuing without waiting won't break anything, but keep in mind results may not be final and you may need to repeat the next step one or more times.
Click the same button again.
Observe the files prefetched in the Network tab to be the same as listed on the page.
Resize the device window to about 600, 800, and 1200 pixels. Click the "Prefetch" button after each change. Observe files prefetched match those listed on the page.
CORS errors may appear temporarily. You can ignore them.