About [[MediaWiki:Apihelp-gather-description/ksh]]
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What is a "Gather collection"? Please explain.
Looks like there is no help page yet, but it's this thing: mw:File:Gather example collection.png. A list of page titles stored in the database, which is rendered as a gallery. The extension sometimes calls them "Gather collections", sometimes "collections", sometimes "lists" and sometimes in other ways. Someone should file a bug to ask consistency, but apparently that's a hot topic for the maintainers.