Hi Chuanchuan Li,
As said by the reference, only 10-bit, 9-bit and 8-bit (10-bit is only supported in UART0) are supported in KL26.
you can not use 7-bit data character.
regarding the question on the attached image, the bit M in UART0 and UART1/2 has the same function. the description for bit M in both chapter mean same thing.
hope it help!