5.5.6 ‘@d’: Define outer macro, and mark

This command begins the definition part.

‘@d’ defines an outer macro (just as ‘@D’ does), and also marks the next identifier as defined in the present section. It is equivalent to

‘@d’ == ‘@D@[’

(see AT[).

The distinction between ‘@d’ and ‘@D’ is analagous to the distinction between ‘@a’ and ‘@A’. See ATa.