docstr: Sets the cell value formatting rule using d3 formatting mini-
  languages which are very similar to those in Python. For
  numbers, see:
  https://github.com/d3/d3-format/tree/v1.4.5#d3-format.
  
  The 'format' property is an array that may be specified as a tuple,
  list, numpy array, or pandas Series
  
  Returns
  -------
  numpy.ndarray
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code: def format(self):
      """
      Sets the cell value formatting rule using d3 formatting mini-
      languages which are very similar to those in Python. For
      numbers, see:
      https://github.com/d3/d3-format/tree/v1.4.5#d3-format.
  
      The 'format' property is an array that may be specified as a tuple,
      list, numpy array, or pandas Series
  
      Returns
      -------
      numpy.ndarray
      """
      return self["format"]
  
imports: from plotly.basedatatypes import BaseTraceHierarchyType
  import copy
label_desc: Use image node_id 9 for calling the Header obj's underlying member method code with example usage: obj.format() and returns: self