vis.3: Try to better describe VIS_SAFE

[des]

Summary

The current text is correct, but fails to draw the reader's attention
to the fact that VIS_SAFE essentially works in reverse, i.e. it exempts
certain characters from being encoded.

While here, fix some markup nits.

MFC after: 1 week

[des]

@adrian could you perhaps look into getting this reviewed and committed upstream?

[markj]

contrib/libc-vis/vis.3

297

Now I'm back to not understanding this flag. This text, and the old one, makes it sound like VIS_SAFE overrides other flags. But it doesn't:

$ hexdump -C space
00000000  20 0a                                             | .|
00000002
$ vis -s space

$ vis -w -s space
\040\012$

And looking at the implementation, it seems that VIS_SAFE just means "don't encode backspace, bell, and carriage return." Those characters are encoded by default.

302

It has no effect on space, tab, or newline.

[des]

rf

[markj]

contrib/libc-vis/vis.3

301

Graphic characters are not affected by this flag either.

[des]

rf