Base class

$EXCEPTION INHERITED std::exception              # public by default
$STREAMABLE PARENT PROTECTED app::Printable

PARENT is a synonym of INHERITED. The access specifier is optional and defaults to PUBLIC. An access specifier with no class name after it is an error:

app.msg:1:28: error: expected a base class name after PUBLIC

OVERRIDE

$EXCEPTION only:

$EXCEPTION INHERITED PUBLIC Exception OVERRIDE whatStr
$EXCEPTION OVERRIDE NONE        # back to What() / what()

Semantics: Reference › $STREAMABLE, $EXCEPTION.