code: def ls(checks):
      
      if checks:
          checks = sorted(get_testable_checks() & set(checks))
  
          for check in checks:
              envs = get_available_tox_envs(check, e2e_only=True)
  
              if envs:
                  echo_success('{}:'.format(check))
                  for env in envs:
                      echo_info(env, indent=True)
  
      else:
          for check in get_configured_checks():
              envs = get_configured_envs(check)
  
              if envs:
                  echo_success('{}:'.format(check))
                  for env in envs:
                      echo_info(env, indent=True)
docs: List active or available environments.