[pro] DEFVARs combined service

[Kazimir Majorinc]

"DEFVAR and DEFPARAMETER do the combined service of

  - in some implementations, recording the "definitional home" of the 
variable
  - declaring the indicated variable special in compiler and runtime
  - assigning the variable (either conditionally, as in DEFVAR, which 
assigns only in the case that the variable is unbound, or 
unconditionally, as in  DEFPARAMETER). "

K. Pitman, comp.lang.lisp, 26. April 2001.

What "recording the definitional home" means? Why "in some 
implementations?"