Represents an operator that obtains a Map entry, an indexed value, a property value, or an indexed property value of an object. The following are the rules for evaluating this operator:

 Evaluating a[b] (assuming a.b == a["b"])
   a is null
     return null
   b is null
     return null
   a is Map
     !a.containsKey (b)
       return null
     a.get(b) == null
       return null
     otherwise
       return a.get(b)
   a is List or array
     coerce b to int (using coercion rules)
     coercion couldn't be performed
       error
     a.get(b) or Array.get(a, b) throws ArrayIndexOutOfBoundsException or IndexOutOfBoundsException
       return null
     a.get(b) or Array.get(a, b) throws other exception
       error
     return a.get(b) or Array.get(a, b)
 
   coerce b to String
   b is a readable property of a
     getter throws an exception
       error
     otherwise
       return result of getter call

   otherwise
     error