What are the fundamental TeX length names, corresponding to trim size and offsets?
I already know that
\pdfpageheight will grab enough information to calculate the PDF MediaBox (in different units). These commands are independent of the latex document class, AFAIK.
And I know that if memoir class is used, I can grab the trim size and offsets from the values set using memoir commands:
\trimedge. These can be used to calculate the size and position of the PDF TrimBox. I know how to do the calculations.
But the problem is that for the TrimBox, I rely on memoir-specific lengths. If memoir is not in use, no luck. So what I want to know is: Is there a universal set of lengths (by name) that latex uses regardless of document class, when it comes to the TrimBox? I don't need to know the values until AtBeginDocument.
Why I wish to know: I have improvements to pdfx package, which enable arbitrary document sizes. But my current solution relies on memoir to give me the lengths. I would like to make it more general.