[…] I myself have never understood why one would want
a browser extension to display an Edit button outside the viewport. It seems unappealing
from a UX perspective and for me personally would likely fade into "banner
blindness" and notice if it were detected and/or notice it too much if it tries to
get my attention on any editable page.
Have you been able to check if screenreader software possibly does
something useful with these rel="…" attributes?
For me this was always the main motivation to provide e.g. meaningful
<link rel="prev"> and <link rel="next"> in addition to the
pagination
links that can be found in the content of a page. Not necessarily to
"display buttons outside of the viewport". But for users with visual
impairments that can't use a mouse, but have dozens of keyboard
shortcuts memorized instead. The fact that these links are displayed
in a toolbar is more secondary. What matters is that they have the
same shortcuts assigned, no matter what the website is.
Even if it turns out that screenreaders are the only tools that do
something with a <link rel="…">, and even if screenreaders only make
up zero point whatnot percent, I believe it's worth it.
Remember, accessibility is a process, not a state you can reach.
Best
Thiemo