Vertical rule using datasets

spec.json

/* Vertical rule using datasets */
{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "datasets": {
        "linedata": [
          {"a": 1, "b": 30},
          {"a": 2, "b": 45},
          {"a": 3, "b": 50},
          {"a": 4, "b": 60},
          {"a": 5, "b": 70},
          {"a": 6, "b": 80},
          {"a": 7, "b": 70},
          {"a": 8, "b": 50},
          {"a": 9, "b": 10}
        ],
        "ruledata": {"ownval":5}
      },
      "layer": [
    {
      "data": {"name": "linedata"},
      "mark": {"type":"line", "size": 2},
      "encoding": {
        "x": {"field": "a", "type": "quantitative"},
        "y": {"field": "b", "type": "quantitative"}
      }
    },
    {
       "data": {"name": "ruledata"},
      "mark": {"type": "rule", "strokeDash": [4, 4], "size": 2, "color": "grey"},
      "encoding": {
        "x": {"field": "ownval", "type": "quantitative"}
      }
    }
  ]
}

https://vega.github.io/editor/#/gist/a9b017cf43f42a63ee099f68c67da3f9/spec.json