It's not "image format file" - it is Scalable Vector Graphics format, there was pageSet in SVG Print draft already. It would be useful because a graphics (text layout) may span several pages, like in PDF.
For example if you had a very tall SVG image, you would constrain the height of the block that it was in, and set the overflow-style to paged-y. The browser would then provide some form of control for you to page vertically through the content in that block.
This stuff is currently documented in the GCPM module, but I suspect it will move somewhere else eventually.
I would consider printing to be another story though. It is possible to have a page size that spans to several pages when printing, but still it represents just one page.
PDF is not the best analogy because it was designed to be a document format from the beginning.
Anyway, I will stop here because this thread is reaching the futile point.