19.2 Pathnames 19.2.2 Interpreting Pathname Component Values 220.127.116.11 Special Pathname Component Values 18.104.22.168.3 :UNSPECIFIC as a Component Value
22.214.171.124.3.1 Relation between component values NIL and :UNSPECIFIC
If a pathname is converted to a namestring,
the symbols nil and :unspecific
cause the field to be treated as if it were empty.
both nil and :unspecific
cause the component not to appear in the namestring.
However, when merging a pathname with a set of defaults,
only a nil value for a component
will be replaced with the default for that component,
while a value of :unspecific
will be left alone as if the field were "filled";
see the function merge-pathnames and Section 19.2.3 Merging Pathnames.