Aircraft Control Language

    Note that the language is meant to be an "instantaneously
    decodable" code, i.e. trivial to parse left-to-right.
    
    In non-expert mode, there should be an indication on-screen
    where we are in the parser.  For instance if you type "x"
    it says "radio" and then if you type "c" it says "comm".
    
    "*" means if you hold the key, the effect continues or repeats.
    
    Repeats are tricky for multi-key commands, which is why the keys
    u, d, l, and r require special treatment.  For example, aarrrr
    gives us +4 units of aileron trim, while arrrlr gives us +2 net
    units of rudder trim.  Therefore these four letters are _reserved_
    and cannot be the first letter of any command in the language.

# High-priority single-key commands:
space                   *push-to-talk
arrow-left arrow-right  *stick left, right
arrow-up arrow-down     *stick fwd(not nose-up!), aft(not nose down!)
-   +                   *throttles less, more
/                       *temporarily disengage mouse from yoke
                          (to see how far out-of-trim we are)
ctrl-G                  no-op aka cancel
esc                     no-op aka cancel

    Note that ctrl-G _or any other single-key command_ cancels any
    parially-entered multi-key command, whereupon you start over at
    the root of the parser.

# Special key
tab             show menu (or submenu) items available
                or hide menu if auto-menu-show was in effect

# Engine menu
eh0  eha        all engines carb heat off, carb heat applied
em0  e2ma       all engines mixture off, engine 2 mixture 100%
ep0  epa        all engines prop rpm minimum, prop rpm max
e1f0 e2fa       engine 1 cowl flaps closed, engine 2 cowl flaps open
e1t0 e2ta       engine 1 throttle closed, engine 2 throttle 100%
e1tu e2td       *engine 1 throttle up a little, down a little
e1i0 e1i1 e1i2 e1i3 engine 1 igniter or magneto none/left/right/both
eb0 eb1 eba     all engines boost pump off, low, high
e1su            *engine 1 starter (start "up")

    Note that where a digit is expected, "a" means either 
    "all" or 10 out of 10 (which is consistent with the
    hex digit "a", so you can interpret it either way).

# Radio menu
xc1f123.00      comm 1 frequency
xc1t            comm 1 toggle standby <--> active
xc1v5 rc1va     comm 1 volume halfway, max
xn2f116.10      nav 2 frequency
xn2o060         nav 2 OBS 060 degrees
xn1v rn1i       nav 1 voice, ident filter
xaf234          adf frequency

    Note we use "x" for radio, since "r" is reserved.
    The mnemonic is Rx/Tx for receive and transmit.
    Or maybe we could use capital R for Radio.

# Airframe menu
ab0 aba         parking brake off, on
ag0 aga         gear retract, gear extend
af0 af1 af2 afa flaps none, 10 degrees, 20 degrees, full
as0 asa         speedbrakes retract, speedbrakes extend
arl arr         *rudder trim left, right
apu apd         *pitch trim down, up
aal aar         *aileron trim left, right
at0 ata         tailwheel lock, unlock

# Switch menu
sm0 sm1 sm2 sm3 master switch off, alt?, batt, alt+batt
sr0 sra         radio master off, on
sl0 sla         landing light off, on
st0 sta         taxi light off, on
sb0 sba         rotating beacon off, on
ss0 ssa         strobes off, on
sp0 sp5 spa     panel lights off, halfway, full
sd0 sda         dome light off, on

# view pan, tilt, zoom ???
# view shift L/R, up/down ???