Bell character support

[tg-x]

From the documentation:

{2:ctrls Control characters}

These are taken to be characters in the ranges [0x00-0x1f] ({b C0}) and
[0x80-0x9f] ({b C1}), and [0x7f] (BACKSPACE). This is the
{{: http://unicode.org/reports/tr44/#General_Category_Values}Unicode
general category} {b Cc}.

As control characters directly influence the cursor positioning, they
cannot be used to create images.

Since the bell character (0x07) does not change the cursor position, it should be allowed in images,
and/or there should be a bell attribute that prints it.

[pqwy]

No, breaks the model. You could detect the rendering strategy, but couldn't control when exactly the bell rings. Bell is a side-effect in the terminal protocol.[*] It's not that it doesn't change the cursor position; it simply doesn't exist in the plane.

A bell attribute has no meaning.

What I might conceivably do, is add a function to Term to ring the bell and set the title. But in the meantime, nothing prevents you from printing 0x07 to ring a bell. You can do that precisely because it does not change the cursor position.

[*] Strictly, all characters are side effects in the terminal protocol. But some are less uniform than the others.