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{  "$schema": "https://vega.github.io/schema/vega-lite/v4.json",  "data": {"url": "data/cars.json"},  "encoding": {    "x": {      "field": "Year",      "timeUnit": "year"    }  },  "layer": [    {      "mark": {"type": "errorband", "extent": "ci"},      "encoding": {        "y": {          "field": "Miles_per_Gallon",          "type": "quantitative",          "title": "Mean of Miles per Gallon (95% CIs)"        }      }    },    {      "mark": "line",      "encoding": {        "y": {          "aggregate": "mean",          "field": "Miles_per_Gallon"        }      }    }  ]}