docs: def repr_single_for_md(s):
      r"""
      Args:
          s (str):
  
      Returns:
          str: str_repr
  
      CommandLine:
          python -m ibeis.templates.generate_notebook --exec-repr_single_for_md --show
  
      Example:
          >>> # DISABLE_DOCTEST
          >>> from ibeis.templates.generate_notebook import *  # NOQA
          >>> s = '#HTML(\'<iframe src="%s" width=700 height=350></iframe>\' % pdf_fpath)'
          >>> result = repr_single_for_md(s)
          >>> print(result)
      """
      import utool as ut
      if True:
          str_repr = ut.reprfunc(s)
          import re
          if str_repr.startswith('\''):
              dq = (ut.DOUBLE_QUOTE)
              sq = (ut.SINGLE_QUOTE)
              bs = (ut.BACKSLASH)
              dq_, sq_, bs_ = list(map(re.escape, [dq, sq, bs]))
              no_bs = ut.negative_lookbehind(bs_)
              #no_sq = ut.negative_lookbehind(sq)
              #no_dq = ut.negative_lookbehind(dq)
  
              #inside = str_repr[1:-1]
              #inside = re.sub(no_bs + dq, bs + dq, inside)
              #inside = re.sub(no_bs + bs + sq, r"\\'", r"'", inside)
              #str_repr = '"' + inside + '"'
              #inside = re.sub(r'"', r'\\"', inside)
              #inside = re.sub(ut.negative_lookbehind(r"'") + r"\\'", r"'", inside)
  
              inside = str_repr[1:-1]
              # Escape double quotes
              inside = re.sub(no_bs + r'"', r'\\"', inside)
              # Unescape single quotes
              inside = re.sub(no_bs + bs_ + r"'", r"'", inside)
              # Append external double quotes
              str_repr = '"' + inside + '"'
          return str_repr
      else:
          return '"' + ut.reprfunc('\'' + s)[2:]