CURLOPT_ABSTRACT_UNIX_SOCKET(3) on macOS
The text def85f804837, as macOS 11.5, macOS 11.4, macOS 11.3, macOS 11.2, macOS 11.1, macOS 11.0.1, macOS 10.15.6, macOS 10.15.5, macOS 10.15.4, macOS 10.15.3, macOS 10.15.2, macOS 10.15.1, macOS 10.15 shipped it.
set an abstract Unix domain socket