Opens a book's source and answers its current contents, or declines.
Remarks
DESIGN-EXTERNAL-LINKS §4D: the default one (phase E) is WorkbookIO.read with
calcOnLoad: 'none', taking the source's own cached values and never evaluating it — that is
what Excel's cache holds, and it keeps A-cites-B-cites-C from becoming a crawl. An extension
point for a source that is not a workbook file. WHETHER a source may be opened at all — an
untrusted file naming an arbitrary path or URL — is the host's decision, made before this is
asked; a resolver never fetches on its own initiative, only on IExternalBook.refresh.
Opens a book's source and answers its current contents, or declines.
Remarks
DESIGN-EXTERNAL-LINKS §4D: the default one (phase E) is
WorkbookIO.readwithcalcOnLoad: 'none', taking the source's own cached values and never evaluating it — that is what Excel's cache holds, and it keeps A-cites-B-cites-C from becoming a crawl. An extension point for a source that is not a workbook file. WHETHER a source may be opened at all — an untrusted file naming an arbitrary path or URL — is the host's decision, made before this is asked; a resolver never fetches on its own initiative, only on IExternalBook.refresh.