Yes, I'm pretty sure by now I know what is meant. Thanks you all. I printed the Elliptical Construction page for weekend special home class.

>..> The difficulty (of making it visible) is due to the fact that the word refers to the absence (omission) of something unspecified.<..< Ha. :~)

Thanks Myridon. I think in the confusion of all those heaped up difficult words I lost track of the visiualizing example.
The example is quite clear.