Because technology (and reality) is deep. Human comprehension is a shallow collection of approximations and simplifications - albeit in different areas for diff

Because technology (and reality) is deep. Human comprehension is a shallow collection of approximations and simplifications - albeit in different areas for different people, but the point is that no one mind is capable of understanding everything anymore. Changing the background color to black looks like redaction, it would be redaction if it were printed out, the average consumer of documents has no idea about the details of ObjStm layering and text selection ordering in a PDF.