/* decoding */
        //// ...
        if (check &
            (ENCODE_PERLQQ|ENCODE_HTMLCREF|ENCODE_XMLCREF)){
            SV* subchar = 
            (fallback_cb != &PL_sv_undef)
		? do_fallback_cb(aTHX_ (UV)s[slen], fallback_cb) 
		: newSVpvf("\\x%02" UVXf, (UV)s[slen]);
            sdone += slen + 1;
            ddone += dlen + SvCUR(subchar);
            sv_catsv(dst, subchar);
            SvREFCNT_dec(subchar);
        } else {
            sdone += slen + 1;
            ddone += dlen + strlen(FBCHAR_UTF8);
            sv_catpv(dst, FBCHAR_UTF8);
        }