The object on which the special actions are to be performed. This cannot be a symbol.
Note that all the current special-free-action functions are performed on the object. Use flag-not-special-free-action to unflag an object.
Each object that is flagged for special free action adds some overhead to every garbage collection. This is not significant for a small number of objects, but calling
flag-special-free-action with a large number of objects may slow the system significantly. Thus you should avoid using special free actions where possible. Normally, they should be used only for objects that keep some external resources which need to be freed.
LispWorks User Guide and Reference Manual - 13 Feb 2015