This function is useful to check if the SOAP call failed, but without using exceptions. To use it, create a SoapClient object with the exceptions option set to zero or FALSE. In this case, the SOAP method will return a special SoapFault object which encapsulates the fault details (faultcode, faultstring, faultactor and faultdetails).
If exceptions is not set then SOAP call will throw an exception on error. is_soap_fault() checks if the given parameter is a SoapFault object.