*** The function set-buffer-multibyte sets the flag in the current
buffer that says whether the buffer uses multibyte representation or unibyte representation. If the argument is nil, it selects unibyte representation. Otherwise it selects multibyte representation.

This function does not change the contents of the buffer, viewed as a sequence of bytes. However, it does change the contents viewed as characters; a sequence of two bytes which is treated as one character when the buffer uses multibyte representation will count as two characters using unibyte representation.

This function sets enable-multibyte-characters to record which representation is in use. It also adjusts various data in the buffer (including its markers, overlays and text properties) so that they are consistent with the new representation.