The following is a list of the various URL style socket transports that PHP has built-in for use with the streams based socket functions such as fsockopen(), and stream_socket_client(). These transports do not apply to the Socket Functions of the Sockets extension.
For a list of transports installed in your version of PHP use stream_get_transports().
That was hard to fetch this page mentioned in note by other user long time ago.
I intended to read Appendix P to find some code examples.
Wondering how to implement custom transport extension for php on our server tto be used with some nowadays technologies research.
https://www.php.net/manual/ru/function.stream-context-create.php#75211