Variable EXTERNAL_LINK_PATH_REL_TYPE`Const`

EXTERNAL_LINK_PATH_REL_TYPE: "http://schemas.openxmlformats.org/officeDocument/2006/relationships/externalLinkPath" = 'http://schemas.openxmlformats.org/officeDocument/2006/relationships/externalLinkPath'

The relationship type a book's own part records for the path it is opened from — what sourceEntryFromPath writes, and what the xlsx reader finds on nearly every book.