When called from FFEXTERN, CVSINGLE has additional options passed using inter-program communication, not on the command-line.  Much of the information that is passed is to avoid CVSINGLE needing to read the FS file.  The following additional parameters and options are passed:

Header/Footer/Margins/FontsizeThe data to be used for Internet Explorer and internal HTTP conversions
DatasourceThe WordMerge Data Source file
Timeout/OpenTimeoutOverall and file-open timeout values
Converter ResolutionDerived from CONVERTER_RES in FS file
Converter Page SizeDerived from CONVERTER_PAGE in FS file
ForceConvertFlag to override check of source and destination file times
String optionsDerived from CVT_XLS_OPTIONS. PPT_COLORTYPE, or GSPDFx variables in FS file, depending on conversion type.
QPDF optionsDerived from QPDF_OPTIONS in FS file
Option LettersAdditional option letters
Destination CodesFlags to indicate the presence of email address, phone number in FS, and what conversions are needed.
Output file timeTimestamp to be applies to output file if needed

Additional Option Letters

JBulk Word Merge
LPDF Attach
PWord Merge No strip

Destination Codes

The following flags are set in the Destination Codes field:

E-Mail PresentTrue if the FS file has a $email_address command
Fax Phone PresentTrue if the FS file has a $fax_phone command
Worker PresentTrue if the FS file has a $worker_box command for job preview
'Image' ContentType PresentTrue if there is an $email_attach command matching a $fax_filename command for the same source document, and it has a content-type which will be created (in CF8GCOVER) from a TIF file.
PreconvertTrue if the FS file is for a job preconvert operation (variable CONVERT_PROOF has a non-zero value).
TIF NeededConversion must directly create a TIF (not via PDF)
PDF NeededConversion must directly create a PDF as a final target
WM DOC NeededWordMerge conversion must save a customised DOC file
Inter PDF NeededConversion must create an intermediate PDF and then create a TIF from it