The latest updates of the most important preflight tools (Enfocus PitStop and Callas pdfToolbox) feature new technologies which allow to substantially leverage the quality of preflight checks. We had to wait long time for such possibilities!
Until now preflight tools could only check for properties of single isolated PDF objects. The classical example is black text which is not overprinting. A corresponding check has also issued an error message if the black text was not placed on top of a color background but over the paper white. In this case it’s irrelevant if the text is overprinting or not! This created a lot of unjustified error message (false positives) which was irritating for the user. This has often led to ignore serious error messages. This is a big problem with the preflight profiles of the Ghent Workgroup and PDFX-ready since they feature many overprint checks.
In the past preflight also checked invisible objects which were masked or covered by other objects.
A restriction of the objects to check was only possible with the page geometry boxes (e.g. BleedBox, TrimBox). A restriction of the preflight to an arbitrary contour (e.g. cutline) was not possible.