What does the Print check measure?

Every page at print size: pure black lines, never under KDP's 0.75 pt, nothing in the margins, every space measured against the readers' limits, every number at least 7 pt. The card also lists the book's page count, whether pages were drawn by an image AI, and notes such as spaces too small for a number, answers in color, or blank pages added. While a problem remains, Export is greyed out.