TerminalSettings.PARMRK (gb.term)

Return or set if input bytes with parity or framing errors are marked when passed to the program.

This bit is meaningful only when INPCK is set and IGNPAR is not set.

The way erroneous bytes are marked is with two preceding bytes, \377 and \0. Thus, the program actually reads three bytes for one erroneous byte received from the terminal. If a valid byte has the value \377, and ISTRIP is not set, the program might confuse it with the prefix that marks a parity error. Therefore, a valid byte \377 is passed to the program as two bytes, \377 \377, in this case.

If neither IGNPAR nor PARMRK is set, read a character with a parity error or framing error as \0.