<FORMAT> is the desired output file format.
Possible values include: csv, json, jsonlines, xml. You can
also implement support for more formats.
Warning
If you export in CSV format, and in your spider code you yield items as Python dictionaries, only the fields present on the first yielded item are exported for all items.
One solution is to customize output fields through the fields feed
option of FEEDS or
through the FEED_EXPORT_FIELDS Scrapy setting to explicitly indicate all
fields to export.
You can alternatively yield something other than a Python dictionary that supports declaring all possible fields, such as an Item object or an attrs object.