Backward Compatible

I'm struggling with a question for the last month, and I would like to 
hear your opinion on it.

* What do we mean when we say backward compatible in the context of the 
Web?
* How would you define it?
* Do you define it with regards
	- to the specifications?
	- to the tools?
	- to the authoring techniques?

Ref:

karl% dict compatible
*** Source: WordNet (r) 2.0 ***
compatible
      3: capable of being used with or connected to other devices or
         components without modification [ant: {incompatible}]

karl% dict backward
*** Source: WordNet (r) 2.0 ***
backward
      adv 1: at or to or toward the back or rear; "he moved back";
             "tripped when he stepped backward"; "she looked
             rearward out the window of the car" [syn: {back}, 
{backwards},
              {rearward}, {rearwards}] [ant: {forward}]



-- 
Karl Dubost - http://www.w3.org/People/karl/
W3C Conformance Manager
*** Be Strict To Be Cool ***