Data formats
Dataformat's are plugins that define how a table of data can be exported for download. Moodle comes with plugins for CSV, Excel, ODS, JSON, and HTML.
Components
dataformat/FORMATNAME/lang/en/format_FORMATNAME.php
Contains the English language strings used in the format. You can also define strings for other languages.
dataformat/FORMATNAME/classes/writer.php
This file is the real meat of the form, it contains class which extends \core\dataformat\base defining how the data stream should be encoded.
dataformat/FORMATNAME/version.php
Version definitions, see version.php. It is highly recommended always to have it and it is required if you have any files in db folder