VegaLite.repeat

You're seeing just the function repeat, go back to VegaLite module for more information.
Link to this function

repeat(vl, repeat_def, child_view)

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Specs

repeat(t(), keyword(), t()) :: t()

Builds a repeated multi-view specification from the given single-view template.

Repeat definition must be either a list of fields or a row/column/layer mapping. Then some channels can be bound to a repeated field using encode_repeat/4.

Examples

# Simple repeat
Vl.new()
|> Vl.data_from_values(...)
|> Vl.repeat(
  ["temp_max", "precipitation", "wind"],
  Vl.new()
  |> Vl.mark(:line)
  |> Vl.encode_field(:x, "date", time_unit: :month)
  # The graphic will be reapeated with :y mapped to "temp_max",
  # "precipitation" and "wind" respectively
  |> Vl.encode_repeat(:y, :repeat, aggregate: :mean)
)

# Grid repeat
Vl.new()
|> Vl.data_from_values(...)
|> Vl.repeat(
  [
    row: [
      "beak_length",
      "beak_depth",
      "flipper_length",
      "body_mass"
    ],
    column: [
      "body_mass",
      "flipper_length",
      "beak_depth",
      "beak_length"
    ]
  ],
  Vl.new()
  |> Vl.mark(:point)
  # The graphic will be repeated for every combination of :x and :y
  # taken from the :row and :column lists above
  |> Vl.encode_repeat(:x, :column, type: :quantitative)
  |> Vl.encode_repeat(:y, :row, type: :quantitative)
)

See the docs for more details.