\fICURLOPT_POSTFIELDS\fP to anything but NULL. When providing data with a
callback, you must transmit it using chunked transfer-encoding or you must set
the size of the data with the \fICURLOPT_POSTFIELDSIZE\fP or
-\fICURLOPT_POSTFIELDSIZE_LARGE\fP option.
+\fICURLOPT_POSTFIELDSIZE_LARGE\fP option. To enable chunked encoding, you
+simply pass in the appropriate Transfer-Encoding header, see the
+post-callback.c example.
You can override the default POST Content-Type: header by setting your own
with \fICURLOPT_HTTPHEADER\fP.