addon.document.exportAllOpen {folder, format?} writes a copy of every
open document to one folder as Save a Copy does, each named after its
document with taken names numbered so no file is replaced. Documents
keep their paths and modified state, the active one stays active, and a
document that can't be written is reported while the others are still
written. Object > Plug-ins > Document Tools gets Export All Open
Documents as PDF and as SVG, which ask for the folder.