Return information about the way Emacs currently reads keyboard input.
The value is a list of the form (INTERRUPT FLOW META QUIT), where
INTERRUPT is non-nil if Emacs is using interrupt-driven input; if
nil, Emacs is using CBREAK mode.
FLOW is non-nil if Emacs uses ^S/^Q flow control for output to the
terminal; this does not apply if Emacs uses interrupt-driven input.
META is t if accepting 8-bit input with 8th bit as Meta flag.
META nil means ignoring the top bit, on the assumption it is parity.
META is neither t nor nil if accepting 8-bit input and using
all 8 bits as the character code.
QUIT is the character Emacs currently uses to quit.
The elements of this list correspond to the arguments of `set-input-mode'. (fn)