Three-stage checkbox

[Barry Levine]

I think someone else already voiced disagreement to the use of a 
three-stage checkbox to indicate "Yes", "No", and "Don't know". I'll 
toss in my two cents, as well.

For a three-stage checkbox to have a line through it, it indicates that 
it encompasses some portion of both the Yes and No states. The example 
given (by another) was the hierarchical checkboxes (like an installer 
program). In the case of a "Don't know", it's -neither- Yes nor No. 
Radio buttons produce the desired modality according to the Apple 
guidelines (which *sigh* even Apple has partially abandoned).

Regards,
Barry