+ it is enclosed by another WITH-COMPILATION-UNIT.
+
+ :SOURCE-PLIST Plist-Form
+ Attaches the value returned by the Plist-Form to internal debug-source
+ information of functions compiled in within the dynamic contour.
+ Primarily for use by development environments, in order to eg. associate
+ function definitions with editor-buffers. Can be accessed as
+ SB-INTROSPECT:DEFINITION-SOURCE-PLIST. If multiple, nested
+ WITH-COMPILATION-UNITs provide :SOURCE-PLISTs, they are appended
+ togather, innermost left. If Unaffected by :OVERRIDE."