[rustdoc] Placeholder for search field makes no sense

Currently rustdoc generated documentation has this for the placeholder of search field:

Click or press 'S' to search, '?' for more options…

Now, the problem here, to summarize, is that this placeholder is not really a placeholder, but rather a call-to-action, half of which is even a feature unrelated to search. Not only this call-to-action won’t be visible with text alraedy entered, it does not really help with identifying the purpose of the field.

I realised this when got to a windows machine for some screen reader tests (for https://github.com/rust-lang/rust/pull/39246) and had the placeholder read out to me. Screen reader, when focused on the field read out:

Click or press S to search, ? for more options editable field

and I realised that this placeholder doesn’t make sense even when I’m able to see the page, much less when I don’t.

I quickly prototyped a potential change and filled this issue so anybody with better ideas could chime in.

1. cc @camlorn

   @nagisa you may want to host that prototype somewhere that you can link (not an image) so that people who need screenreaders can try it.

   Alex Burka at 2017-01-23 23:34:43

2. @durka I prototyped that with devtools, so no actual thing I could host.

   Simonas Kazlauskas at 2017-01-23 23:39:18

3. I don't see a potential issue here, as long as it's set to something. Though those keys should be advertised somewhere if they do actually do useful things.

   Is there an actual visible label for the searchbox with placeholder? One good rule of thumb is that if HTML5 adds a visible label, some (hopefully all, but I'm not counting on it) of the screen readers will pick it up.

   Austin Hicks at 2017-01-24 22:08:26

4. triage: no change

   Steve Klabnik at 2019-12-05 23:55:28