code: def remove_reference_line_marker(line):
      
      # Get patterns to identify reference-line marker patterns:
      marker_patterns = get_reference_line_numeration_marker_patterns()
      line = line.lstrip()
  
      marker_match = regex_match_list(line, marker_patterns)
  
      if marker_match is not None:
          # found a marker:
          marker_val = marker_match.group(u'mark')
          # trim the marker from the start of the line:
          line = line[marker_match.end():].lstrip()
      else:
          marker_val = u" "
      return (marker_val, line)
docs: Trim a reference line's 'marker' from the beginning of the line.
         @param line: (string) - the reference line.
         @return: (tuple) containing two strings:
                   + The reference line's marker (or if there was not one,
                     a 'space' character.
                   + The reference line with it's marker removed from the
                     beginning.