Bradley pointed out that they appear in an example in SRFI 268 and
thinks it is a bad idea.  I decided to investigate what Schemes do
that support @vector literals, as SRFIs 4 and 160 don't say one way or
the other.  Gambit and Skint do not support it, Chicken (if you import
SRFI 4) and Chibi do.

I've changed my draft to remove them.