class_docstr: A markdown cell, that's been preprocessed (e.g. parsed into a Markdown AST).
code: def __init__(self, cell):
      source = cell_source(cell)
      self.metadata = cell.metadata
      self._lines = source.splitlines()
  
      self.ast = COMMONMARK_PARSER.parse(source)
      # make sure we don't have to deal with '<text><text>' elements
      self.ast.normalize()
  
imports: import argparse
  import commonmark
  import nbformat
  import os
  import re
  import subprocess
  import sys
  import textwrap
  from pathlib import Path
label_desc: Use image node_id 1 to create a new MarkdownCell object  with example: obj = MarkdownCell(cell)