Visibility: Object is partially obliterated
The property "Object is partially obliterated" detects objects that are partially obliterated by other objects (and are thus only partially visible on the page). An object is considered partially obliterated in this context if at least one other opaque object (i.e. neither overprinting nor transparent) is above it and overlaps it, thus partially suppressing rendering of that object in the overlap area.
For detecting complete obliteration see the article Visibility: Object is completely obliterated.
The "Filter" option defines the set of objects for which it shall be determined whether they are partially obliterated.
The example below makes use of the check Object is partially obliterated.kfpx and the PDF file three red rectangles, one half obliterated, one fully obliterated.pdf which are available for download:
The page shown in the screenshot below contains three evenly spaced red squares, where the middle one is half obliterated, and the rightmost one is fully obliterated (and thus not visible).
It can be seen below how the partially obliterated (and thus only partially visible) red square in the middle is detected.