[ #00 ]
^ Operator
  ^ Operator
   ^^ Number
      ^ Operator
[[ #00 ]]
^^ Type
   ^ Operator
    ^^ Number
       ^^ Type
[x #00 ]x
^^ Type
   ^ Operator
    ^^ Number
       ^^ Type
x[x #00 x]x
^^^ Type
    ^ Operator
     ^^ Number
        ^^^ Type