Property Identifier
Identifier
Gets or sets the value written as dc:identifier, or null to derive one from the
content — the default.
public string? Identifier { get; set; }Property Value
Remarks
EPUB requires a unique identifier and the determinism rules forbid generating a fresh one, which would make two writes of the same document differ. The default is therefore derived from the bytes of the content documents themselves: identical input yields an identical identifier, different input yields a different one, and nothing ambient is involved.
A publisher who owns an ISBN or a permanent URN sets it here, and should: a content-derived identifier changes when the content does, which is the wrong behaviour for something meant to name a work across its editions.