Display-list space: the same coordinates
RitoArtifact.displayList paints in, spread page offset and page
margins included. Hit-test taps on the painted surface directly
against this — no host-side margin correction.
Canonical footnote key when this hit is a semantic noteref — the
engine's own href#fragment form. Pass it to
RitoReaderSession.readFootnote verbatim; a host must not
normalize the link href itself. Null means an ordinary link.
True while this key's definition has not been indexed yet. The key
is already valid; reading it fails until background indexing
reaches the definition, so a host can show the popup with a
loading state and retry.
