Let me refer you to the documentation:
https://zorro-project.com/manual/en/ccy.htmNotice that ccyIdx() is not documented. This is intentional. The script writer is not supposed to access it, since it is a helper function designed for the documented functions to use from Zorro's backend.
Really, the source code for ccyIdx is for your reference only. It's already compiled.
Scroll down to the bottom of the page to see an excellent example of how to use the currency strength functions from the script-side. It loops through your forex assets (pairs like "EUR/USD"), and it generates strength values for all currencies (like "USD" or "EUR"). Then it selects a strongest and weakest pair based on those values. Then it goes long on the strongest pair and short on the weakest pair, given a minimum strength threshold value is crossed.
