expression: '//'
expected: |-
  {"type": "EXPRESSION_NODE", "start": 0, "end": 2, "nodes": [
    {"type": "ALTERNATION_NODE", "start": 0, "end": 2, "nodes": [
      {"type": "ALTERNATIVE_NODE", "start": 0, "end": 0, "nodes": []},
      {"type": "ALTERNATIVE_NODE", "start": 1, "end": 1, "nodes": []},
      {"type": "ALTERNATIVE_NODE", "start": 2, "end": 2, "nodes": []}
    ]}
  ]}