The source entry Excel would record for a path a user typed — the inverse of
externalBookClosedName's directory half, so a minted book displays back as it was typed.
A Windows path becomes a file:/// URI with forward slashes and percent-encoding, a UNC path a
file://server/share/… one, and a URL or a bare relative name is kept verbatim — the three
target shapes measured in the corpus (DESIGN-EXTERNAL-LINKS §2.2).
The source entry Excel would record for a path a user typed — the inverse of externalBookClosedName's directory half, so a minted book displays back as it was typed.