<p>or the name of a DEFSTRUCT created accessor for a slot whose declared type is
either FIXNUM or T. Results are unspecified if the slot has a declared type
other than FIXNUM or T.</p>
<p>In case of SLOT-VALUE, if the slot is unbound, SLOT-UNBOUND is called unless
OLD is EQ to SB-PCL:+SLOT-UNBOUND+ in which case SB-PCL:+SLOT-UNBOUND+ is
returned and NEW is assigned to the slot. Additionally, the results are
unspecified if there is an applicable method on either
SB-MOP:SLOT-VALUE-USING-CLASS, (SETF SB-MOP:SL