Reference information for DFHWBEP, Web error program has a listing and technical descriptions of all the parameters in the COMMAREA passed to DFHWBEP.
If you change the message body, you do not need to calculate the body length or change the Content-Length header. On return to CICS, specify the length of the buffer containing the complete message. CICS checks the length of the message body that you have provided, and corrects the Content-Length header accordingly.
The default HTTP response is passed to DFHWBEP in the EBCDIC code page 037. CICS assumes that the HTTP response addressed by WBEP_RESPONSE_PTR on exit from the Web error program is also in EBCDIC, and performs code page conversion on the response to convert it to a suitable ASCII character set before returning it to the client. If an analyzer program is involved in the processing path and has set parameters for code page conversion (as individual server and client code page parameters, or as a DFHCNV key), CICS uses these options for code page conversion. If no analyzer program is involved, or the analyzer was not invoked before the error occurred, the ISO-8859-1 character set is used for the response.