This error handler takes the ztd::text::encoding_error::incomplete_sequence error and uses it to read from the provided "progress" contiguous range provided as the third parameter to any error handler. This can be helpful in situations here incomplete input is not to be interpreted as an error, such as in situations with networking stacks, I/O reads (particularly, non-recoverable streams like std::istream_iterators or std::ostream_iterators), and other such storage cases.
The data read but not used from an incomplete error during encode and decode operations is stored in the basic_incomplete_handler object and can be accessed VIA the code_points and code_units functions.
ztd::text::basic_incomplete_handler