Arbitrary information, defined during
controlblock creation.
unsigned char *outString
Buffer with characters to write.
int outLen
Number of characters in buffer.
Tcl_Interp *interp
Interpreter for error messages
(NULL possible).
DESCRIPTION
Procedures of this type are called by an encoder/decoder to write
(partial) transformation results, decoupling the final destination
from result generation. Return value is a standard tcl error code. In
case of failure and interp not NULL an error message should be left
in the result area of the specified interpreter.