code: def xisabs(filename):
    
    if filename.startswith(b'/'):     # Linux/Unix
      return True
    elif filename.startswith(b'\\'):  # Windows
      return True
    elif re.match(b'\\w:[\\\\/]', filename): # Windows
      return True
    return False
docs: Cross-platform version of `os.path.isabs()`
        Returns True if `filename` is absolute on
        Linux, OS X or Windows.