class_docstr: DataFrame Accessor & Method for creating Vega-Lite visualizations.
  
  Examples
  --------
  >>> df.vgplot.line()  # doctest: +SKIP
  >>> df.vgplot.area()  # doctest: +SKIP
  >>> df.vgplot.bar()  # doctest: +SKIP
  >>> df.vgplot.barh()  # doctest: +SKIP
  >>> df.vgplot.hist()  # doctest: +SKIP
  >>> df.vgplot.kde()  # doctest: +SKIP
  >>> df.vgplot.density()  # doctest: +SKIP
  >>> df.vgplot.scatter(x, y)  # doctest: +SKIP
  >>> df.vgplot.hexbin(x, y)  # doctest: +SKIP
  
  Plotting methods can also be accessed by calling the accessor as a method
  with the ``kind`` argument: ``df.vgplot(kind='line', **kwds)``
  is equivalent to ``df.vgplot.line(**kwds)``
docstr: Area plot for DataFrame data
  
  >>> dataframe.vgplot.area()  # doctest: +SKIP
  
  Parameters
  ----------
  x : string, optional
      the column to use as the x-axis variable. If not specified, the
      index will be used.
  y : string, optional
      the column to use as the y-axis variable. If not specified, all
      columns (except x if specified) will be used.
  stacked : bool, optional
      if True (default) then create a stacked area chart. Otherwise,
      areas will overlap
  alpha : float, optional
      transparency level, 0 <= alpha <= 1
  var_name : string, optional
      the legend title
  value_name : string, optional
      the y-axis label
  width : int, optional
      the width of the plot in pixels
  height : int, optional
      the height of the plot in pixels
  ax: altair.Chart, optional
      chart to be overlayed with this vis (convinience method for `chart1 + chart2`)
  
  Returns
  -------
  chart : alt.Chart
      altair chart representation
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code: def area(
      self,
      x=None,
      y=None,
      stacked=True,
      alpha=None,
      var_name="variable",
      value_name="value",
      width=450,
      height=300,
      ax=None,
      **kwds,
  ):
      """Area plot for DataFrame data
  
      >>> dataframe.vgplot.area()  # doctest: +SKIP
  
      Parameters
      ----------
      x : string, optional
          the column to use as the x-axis variable. If not specified, the
          index will be used.
      y : string, optional
          the column to use as the y-axis variable. If not specified, all
          columns (except x if specified) will be used.
      stacked : bool, optional
          if True (default) then create a stacked area chart. Otherwise,
          areas will overlap
      alpha : float, optional
          transparency level, 0 <= alpha <= 1
      var_name : string, optional
          the legend title
      value_name : string, optional
          the y-axis label
      width : int, optional
          the width of the plot in pixels
      height : int, optional
          the height of the plot in pixels
      ax: altair.Chart, optional
          chart to be overlayed with this vis (convinience method for `chart1 + chart2`)
  
      Returns
      -------
      chart : alt.Chart
          altair chart representation
      """
      df = unpivot_frame(
          self._data, x=x, y=y, var_name=var_name, value_name=value_name
      )
  
      x = df.columns[0]
  
      if alpha is None and not stacked and df[var_name].nunique() > 1:
          alpha = 0.7
  
      chart = (
          self._plot(
              data=df,
              width=width,
              height=height,
              title=kwds.pop("title", ""),
              figsize=kwds.pop("figsize", None),
              dpi=kwds.pop("dpi", None),
          )
          .mark_area()
          .encode(
              x=_x(x, df),
              y=alt.Y(
                  value_name,
                  type=infer_vegalite_type(df[value_name]),
                  stack=(None, "zero")[stacked],
              ),
              color=alt.Color(
                  field=var_name, type=infer_vegalite_type(df[var_name])
              ),
          )
      )
  
      if alpha is not None:
          assert 0 <= alpha <= 1
          chart = chart.encode(opacity=alt.value(alpha))
  
      if ax is not None:
          return ax + chart
  
      warn_if_keywords_unused("area", kwds)
      return chart
  
imports: import numpy
  import pandas
  import altair
  from ._utils import infer_vegalite_type, unpivot_frame, warn_if_keywords_unused, validate_aggregation
  from ._pandas_internals import PandasObject, register_dataframe_accessor, register_series_accessor
label_desc: Use image node_id 4 for calling the FramePlotMethods obj's underlying member method code with example usage: obj.area(x, y, stacked, alpha, var_name, value_name, width, height, ax) and returns: chart, unknown