Links, data sources, IDML package links and book chapters go through
io::document_path (craft-docpath) before they reach the file system:
relative paths resolve beside the document, and paths to other computers,
devices and URLs are missing, with the reason in links.list and Preflight.
IDML and INDD packages read a linked file where its link points on this
computer, then from the link's trailing names beside the package, only
when it is a regular file up to 256 MB holding an image or a graphic. A
file URI that names a host keeps it as a network path.
