A dspec is one of:
A symbol which is used as a dspec always names a function or a macro.
(setf foo) is a name for a setf function.
nil is not a legal dspec, because it cannot have a function definition. Therefore when a dspec API returns
nil, this should be interpreted in the usual way as "not found" or "not applicable".
(dspec-class primary-name . qualifiers)
where dspec-class in the canonical name of the class, and qualifiers is a proper list. primary-name is typically a symbol, but can be a list (in the case of a
setf function) or a string (in the case of a package). The equality for canonical dspecs is
Functions in the dspec API accept non-canonical dspecs. All dspec functions, except
dspec:prettify-dspec, find-dspec-locations, name-definition-locations, dspec-definition-locations and find-name-locations return canonical dspecs.
LispWorks User Guide and Reference Manual - 13 Feb 2015