The documentation is very impressive. Note: the current EndNote output style for Refman (RIS) now includes the L1 - `File Attachments|` in all document types! Whether they know it or not, this may make it easier for people to move to Zotero! Another thing to look for is the status of the fields beginning Custom 1 to Custom 7. I have a habit changing Journal Articles and other commonly used field types to Custom 1 through 7, standandarizing my templates for each article type in a way that overwrites data elements I rarely use. This enables me to park various kinds of things like "chapter number" in say Custom 4 and so forth. I would have to be sure to edit Refman to do this, but my simple question pending my diving into the details of the incredible Zotero documentation is whether I can "mirror" Custom 1 to 7 in Zotero and then be able to imprort my data in a way that creates and equivalent Custom 1 to 7 field structure in Zotero.
Data in those fields will get stored in attached notes to the Zotero items. You can modify the .RIS import translator for Zotero if needed to get them automatically placed in specific actual Zotero fields, but this can be a bit involved, so I'd recommend just copying the data out of the notes if needed, unless getting such data added to a specific field is absolutely necessary.
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https://www.zotero.org/support/kb/importing_records_from_endnote