The entire page
The function does not exist
No function called
To be clear, while there is a plan to remove it from the specs (https://github.com/whatwg/html/pull/3872) this method is implemented in Firefox as the compatibility table states.
On a lower note, it's also accessible in Chromium under the "Experimental Web Platform features" flag.
So stating "The function does not exist" doesn't seem entirely correct.
I believe MDN should wait to see how https://github.com/whatwg/html/pull/3872 evolves and if this method is indeed removed from the specs, then a deprecation note should be added to this page.
I'd argue being under a flag is hardly "it exists". It doesn't exist in firefox without a flag (if it does at all) so the compatible table is wrong.
If the page is not going to be removed it should be marked as not available except with special flags
It's available in Firefox without a flag, only Chrome hides it behind a flag. The table is right.