Example of usage=source

gistfile1.txt

curl https://api.stripe.com/v1/tokens \
   -u YOUR_API_KEY: \
   -d bank_account[country]=US \
   -d bank_account[currency]=usd \
   -d bank_account[account_holder_type]=individual \
   -d bank_account[routing_number]=110000000 \
   -d bank_account[account_number]=000123456789 \
   -d usage=source
   
Returns:
{
  "error": {
    "type": "invalid_request_error",
    "message": "You must provide the full name of the bank account holder.",
    "param": "bank_account[name]",
    "type": "invalid_request_error"
  }
}