As series expand, you often get books, novellas or derivative works that are set in the same universe but don't fit into the chronology of the main series of books. Calibre unfortunately has no way of recognising this.
I wanted to check out how this is handled in metadata but can't find the MOBI specification as it seems that with EPUB superseding it, links to it have been orphaned. The EPUB specification doesn't inherently support series information, instead relying on the standard metadata property extension. I'm guessing that this relies on unofficial standard names, so that's not much help either.
Calibre handles series information with the following fields:
Code:
<meta content="TITLE" name="calibre:series"/>
<meta content="INDEX" name="calibre:series_index"/>
Ideally, I'd like to see the series_index field being made optional. Currently I assign in-universe books that are not part of the main chronology index 0. This works for the most part but is not a perfect solution.
I've looked into templates to remove the number when saving books to a device but that is proving to be harder than I anticipated. Similarly, adding a custom "universe" metadata field causes problems when creating a title for books that have both a series and universe field. You'd get things like "Discworld - Discworld 01 - The Colour of Magic" which won't fit on most devices.
While I'm hoping that this might be introduced in Calibre somewhere down the line, I'd also welcome any input or thoughts you might have on this, in relation to both Calibre and the MOBI and EPUB formats.