Flips a top-left-origin box (the stored space) into the PDF-native bottom-left-origin
space pdf-lib draws in, and vice versa. The returned y is the box's bottom edge
measured up from the page bottom — exactly what drawRectangle/drawText expect. Its
own inverse: applying it twice with the same page height returns the original box.
Flips a top-left-origin box (the stored space) into the PDF-native bottom-left-origin space pdf-lib draws in, and vice versa. The returned
yis the box's bottom edge measured up from the page bottom — exactly whatdrawRectangle/drawTextexpect. Its own inverse: applying it twice with the same page height returns the original box.