Craft criteria for asset folders
Check /vendor/craftcms/cms/src/models/FolderCriteria.php Class for reference. I guess most of craft's documentation lies in code.

Or you can visit https://docs.craftcms.com/api/v3/craft-models-foldercriteria.html
which is the same thing.

check table "yourprefix_volumefolders" for data type of FolderCriteria.