> I know what ifdef does (the example below shows me using it)...
>
> //#declare text2use = 2;
>
> box     {
>          <-10,0,11>,<10,10,10>
>
>          #ifdef(text2use)
>                  texture { pigment { White } }
>          #else
>                  texture { pigment { Green } }
>          #end
>
>          }
>
> .... but I'm struggling to understand when you would use it. Why would you refer
> to a variable you've not defined?  Isn't that just sloppy coding.
>
> Has anyone got/had a real-use case for this command? I'd love to know what I'm
> missing out on.
>
>

It's often used in includes. Some uses are:

Make sure that you don't re-parse a file that's been included before. 
Take a look at the base includes, they all have this construct:
#ifndef(Include_File_Flag)
#declare Include_File_Flag=version;
...body of the include file goes here...
#end

Have some defaults parameters that you can optionaly define before 
calling an include or a macro.



Alain

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