docs: def column_definition(table_name, col_name):
      """
      Get the source of a column function.
  
      If a column is a registered Series and not a function then all that is
      returned is {'type': 'series'}.
  
      If the column is a registered function then the JSON returned has keys
      "type", "filename", "lineno", "text", and "html". "text" is the raw
      text of the function, "html" has been marked up by Pygments.
  
      """
      col_type = orca.get_table(table_name).column_type(col_name)
  
      if col_type != 'function':
          return jsonify(type=col_type)
  
      filename, lineno, source = \
          orca.get_raw_column(table_name, col_name).func_source_data()
  
      html = highlight(source, PythonLexer(), HtmlFormatter())
  
      return jsonify(
          type='function', filename=filename, lineno=lineno, text=source,
          html=html)