To export one function, pass the function name into this parameter as
a string.
To export several functions, pass an array of function names.
To export all the functions, pass a special constant SOAP_FUNCTIONS_ALL.
Nota:
functions must receive all input arguments in the same
order as defined in the WSDL file (They should not receive any output parameters
as arguments) and return one or more values. To return several values they must
return an array with named output parameters.