code: def md_filepath(self):
          
          if self.md_node is None: return "MD_FILE_DOES_NOT_EXIST"
          if isinstance(self.md_node, FileNode): return self.md_node.filepath
  
          path = self.md_node.outdir.has_abiext("MD")
          return path if path else "MD_FILE_DOES_NOT_EXIST"
docs: Returns (at runtime) the absolute path of the input MD file.