content: ' or expr
  true OR false Or a or b
  ' and expr
  a and b And c AND d
  ' comp expr
  1 > 2 < foo = bar >= baz <= 42! <> c
  ' bit shift expr
  a >> b << c
  ' add expr
  a + b - c
  ' mul expr
  a * c / b \ d mod 2
  ' unary expr
  -a : +b : not false
  ' increment decrement expr
  a-- : b++
  ' exponential expr
  a ^ b
  ' member ref expr
  foo.bar.baz
  foo@bar.baz
  ' index access expr
  foo.bar["baz"]
  ' anon function expr
  a = function(x, y) : return x + y : endfunction
  b = function(x, y)
      return x - y
  endFunction
  ' call expr
  baz()
  foo.baz(42)
  foo.baz["bar"](a, b)
  ' identifier ref expr
  myvar$
  mydouble#
  ' paren expr
  ()
  ((a + b) * (b - a)) ^ (d mod 2 * not a)