Hi, I'm building out an app where users can annotate PDF:s using PDFKit. For example, the user can activate a highlighting mode, which adds a UIPanGestureRecognizer to the PDFView used to display the document that tracks the user's finger across the screen should a pan start. In this case, panning across text on a PDF document adds selection annotations (of class PDFAnnotation) of type highlight between the start point and the end point of the pan. Now to my question: I have an environment variable named "CG_PDF_VERBOSE" set in my target scheme (since it's been recommended to me in order to track potential issues by previous, automatic console logs), and while I pan across the document adding these annotations to the PDF, I constantly get the message "non-isolated groups aren't supported" logged to the console. What does this message mean, and what should my next steps in debugging the issue be?