   *  - The absolute simplest filter is: .
   *    This is a filter that takes its input and produces it unchanged as output. That is, this is the identity operator.
   *
   * Object Identifier-Index: .foo, .foo.bar
   * - The simplest useful filter is: .foo
   *   When given TOML as an input, it gets the value in the table row "foo"
   *
   * Optional Object Identifier Index: .foo?
   * - Just like .foo, but does not output even an error when . is not an array or an object.
   *
   * Generic Object Index: .[<string>]