> On TCL 9.0, the output is truncated at the first error position.

That's what I expect. Good!

I wouldn't be surprised if the TCL_ENCODING_STOPONERROR flags (or the absence of the TCL_ENCODING_NOCOMPLAIN flag in Tcl 9.0) whould still be handled wrong in the shift-jis encoding: This flag was present, but not accessible on the script level, so it was never tested well.

For TIP #633, I would suggest to introduce a new flag TCL_ENCODING_STRICT, which has the value 0x44 in Tcl 8.7 (so both TCL_ENCODING_STOPONERROR and TCL_ENCODING_NOCOMPLAIN are set, which is - for now - an impossible situation). When using "-strictencoding 1", those flags will be given to the encoder, which takes care of the rest.

Anyway, still work to do .....