'occluded' dialog - make 'unspecified' the default

people are lazy, assume this.. the entry for 'occluded' should default to unspecified, because unless you actually click one or the other, you don't know if it is or isn't. It's also not immediately clear if you're supposed to highlight the area the object *would* cover (including it's occlusion), or just it's pixels that show through

Start by locating the JavaScript code that creates the “occluded” dialog and tracing how its initial selection is set. Confirm that an untouched entry remains “unspecified,” and determine how the dialog should clarify whether highlighting includes the object’s occluded area or only visible pixels.

Written by the indexing model from the issue text.