def is_marker(txt_row):
    """ Determines if the text line contains a program data marker, 
    which is just a single "%" character.
    Args:
      txt_row (string): text line to check.
    Returns:
      True if this text row is a program data marker, False if not.
    """
    if (len(txt_row) < 1):
        return False
    
    if (txt_row[0] == "%"):
        return True
    
    return False