[spec] Clarify purpose of alt-text

[Solene Rapenne]

On Sun, 28 Feb 2021 10:25:25 -0600
Devin Prater <r.d.t.prater at gmail.com>:

> This is my main issue: screen readers *do not* skip the block. This will
> need to be dealt with by the client, not the screen reader.
> 
> On 2/28/21 9:06 AM, Adnan Maolood wrote:
> > This would mean that should a screen reader encounter a preformatted text
> > block with a non-empty alt text, the alt text would be read aloud and the
> > preformatted block would be skipped. After all, that's what "alternative
> > text" is supposed to mean.  

When using the screen reader, can you tell it to skip n lines?

I see something that could be done in clients as an option (not a default)

For this kind of block for example:

```this is something
some text on multiples lines
```

the client could replace it by a link entry accessing a "virtual" page containing only the text, or opening $PAGER on the content.

=> verbatim-text-#1 [Virtual page] This is something

In case of no alt text this would be seen as

=> verbatim-text-#10 [Virtual page] No alt text

of course, the wording Virtual page is the first thing that came out but I'm pretty sure something better could be found.