You're seeing just the function exclusive_maximum, go back to PhoenixSwagger.Schema module for more information.
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exclusive_maximum(model, exclusive?)

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Boolean indicating that value for maximum is excluded from the valid range.

When true: x < maximum, when false: x <= maximum


iex> alias PhoenixSwagger.Schema
...> %Schema{type: :number}
...> |> Schema.maximum(128)
...> |> Schema.exclusive_maximum(true)
  type: :number,
  maximum: 128,
  exclusiveMaximum: true