A exchange symbol (e.g. US). You can find all tickers for a particular exchange with get_tickers(). Be aware that, for US companies, the exchange symbols is simply "US"
cache_folder
A local directory to store cache files. By default, all functions use a temporary path, meaning that the caching system
is session persistent (it will remove all files when you exit your R session). If you want a persistent caching system, simply point argument
cache_folder to a local directory in your filesystem. Be aware, however, that a persistent cache will not refresh your data for new api queries.