docs: def detect_terminal(_environ=os.environ):
      """
      Detect "terminal" you are using.
  
      First, this function checks if you are in tmux, byobu, or screen.
      If not it uses $COLORTERM [#]_ if defined and fallbacks to $TERM.
  
      .. [#] So, if you are in Gnome Terminal you have "gnome-terminal"
         instead of "xterm-color"".
  
      """
      if _environ.get('TMUX'):
          return 'tmux'
      elif subdict_by_key_prefix(_environ, 'BYOBU'):
          return 'byobu'
      elif _environ.get('TERM').startswith('screen'):
          return _environ['TERM']
      elif _environ.get('COLORTERM'):
          return _environ['COLORTERM']
      else:
          return _environ.get('TERM')