How are Authorize.net Silent Post refunds identified?

I have successfully integrated the Silent Post feature with our system for ARB subscriptions. What I am now trying to do is when we refund a payment via the merchant i开发者_如何学Pythonnterface, how do I distinguish a refund from all other transactions? Is the a special variable that is set for a refunded payment?

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x_type will be set to "credit"

Here is an actual Silent Post verifying that (sensitive info is removed/changed)

Array
(
   [x_response_code] => 1
   [x_response_subcode] => 1
   [x_response_reason_code] => 1
   [x_response_reason_text] => This transaction has been approved.
   [x_auth_code] => 056187
   [x_avs_code] => P
   [x_trans_id] => 2692444422
   [x_invoice_num] => 123
   [x_description] =>
   [x_amount] => 59.90
   [x_method] => CC
   [x_type] => credit
   [x_cust_id] => 1234
   [x_first_name] => John
   [x_last_name] => Smith
   [x_company] =>
   [x_address] =>
   [x_city] =>
   [x_state] =>
   [x_zip] =>
   [x_country] =>
   [x_phone] =>
   [x_fax] =>
   [x_email] =>
   [x_ship_to_first_name] =>
   [x_ship_to_last_name] =>
   [x_ship_to_company] =>
   [x_ship_to_address] =>
   [x_ship_to_city] =>
   [x_ship_to_state] =>
   [x_ship_to_zip] =>
   [x_ship_to_country] =>
   [x_tax] => 0.0000
   [x_duty] => 0.0000
   [x_freight] => 0.0000
   [x_tax_exempt] => FALSE
   [x_po_num] =>
   [x_MD5_Hash] => 2A4A7F63DB4390A317E4988430FFA4
   [x_cvv2_resp_code] =>
   [x_cavv_response] =>
   [x_test_request] => false
)