Version 0.8.0 of the CapyPDF library has been released. The main new feature is support for form XObjects and printer's mark annotations.
Printer's marks are things like color bars, crop marks and registration marks (also known as "bullseye marks") that high end printers need for quality control. Here is a very simple document.
An experienced print operator would use the black lines to set up paper trimming. Traditionally these marks were drawn in the page's graphics stream. This is problematic because nowadays printers prefer to use their own custom marks instead of ones created by the document author. PDF solves this issue by moving these graphics operations to separate draw contexts (specifically "form XObjects", which are not actually forms, though they are XObjects) that can then be "glued" on top of the page. These annotations are shown in PDF viewer applications but they are not printed. I have no experience with high end RIP software, but presumably the operator can choose to either print the document's annotations or replace them with their custom QA marks.
As usual, to find out what features CapyPDF has and how to use them, look up either the public C header or the Python code used in unit tests.
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