How to generate file permissions for srw-rw- in the environment of Linux?

found such a previously unnoticed permission in a directory in Linux:
srw-rw- .

I know:

r=4
w=2
x=1

so that if you ignore the beginning s , then two pairs of rw should mean that the owner and the group are readable and writable, but not executable, and others do not have permission to the file.

on a website that demonstrates and calculates chmod online has been tried many times, and even after the addition of suid, it can only generate:
-rwSrwS-
and the result S is not only uppercase, it does not appear in the first place.

I don"t know much about s and t, but I can"t find the first explanation and explanation of s in the command and example of querying chmod on the Internet.
I would like to ask the first bit, s, what is the meaning of such a permission, and how is it generated through the chmod command?

File-permission linux

Jun.03,2021

The

permission bit has only nine digits, the first character represents the file type, s refers to the unix domain socket file, and there is a description in man ls

based on the answer of @ jokester , I tried the following.
mkdir chmodTest & & cd $_ & & touch demofile & & ls-lh generates a file demofile , and the result is as follows:
-rw-r--r-- 1 root root 0 Sep 7 22:23 demofile
and then set UID, chmod 4755 demofile & & ls-lh to generate the following result:
-rws r-xr-x 1 root root 0 Sep 7 22:23 demofile
s appears but not in the first place.

then look for man's description of ls on @ Feng_Yu , but can't find it. However, you can see instructions and examples at the bottom of the following link page, as well as descriptions of several other letters, such as d , c , and so on. @ Feng_Yu gives the correct answer, thank you.
http://www.linuxnix.com/file-.

socket file type

if there is setuid/gid and there is no corresponding x, it will be displayed as S (+ x will become s)

For the meaning of

s, please see man chmod

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