Creates a new EDI transaction set header on the current document.
The 'callback' parameter specifies a function which will be called when the operation completes (or an error is encountered). If the 'callback' parameter is not specified, then the method will block and will not return until the operation completes (or an error is encountered).
The callback for this method is defined as:
'err' is the error that occurred. If there was no error, then 'err' is 'null'.
'err' has 2 properties which hold detailed information:
When called, a new transaction set start (ST or UNH) segment is created and set as the current segment. You should then set the values on said segment before adding creating transaction data segments.
The Code argument should specify the transaction code you want to create (for example, "850" or "INVOIC"). This value, together with the EDI specification and the version provided in the StartInterchangeHeader method are used to locate a matching transaction set schema on the components schema cache. You must make sure that a corresponding schema has been successfully loaded into the component by using the LoadSchema method before trying to call StartTransactionHeader.