where does dash-let save data

I would like define a custom dash-let to let the user select one default account.
I tried to learn from jotlot dash-let but still confusing?

so

  1. how does dash-let save user’s selection? in file or database? what is the path or table name?

  2. if the user selected a default account, how can I pass the account_id to my customized pages? through $_REQUEST? or …