PHP Novice Ask a function solution

PHP Novice Ask a function
I was looking at the source of a little doubt, first there is such a function
function Submitcheck ($var = "") {
if (empty ($_post)) {
return false;
}

if ($_server[' request_method ') = = ' POST ' && (Empty ($_server[' http_referer ') | |
Preg_replace ("/https?:\ /\/([^\:\/]+). */i "," \\1 ", $_server[' http_referer ']) = = Preg_replace ("/([^\:]+). */"," \\1 ", $_server[' Http_host '])) {
return true;
}
else{
return false;
}
}
What is this function for, a simple answer, thank you.
Also, the return value of this function is Boolean, but why do I find such a call in the following: Submitcheck (' islogin ') = = ' yes ' and can be run

------Solution--------------------
You sent two of the same questions at a sudden?
------Solution--------------------
Submitcheck is looking at the delivery of the post through the non-null, and the source of access is the server (the running server of the program),
Then, the function results return true, otherwise the return false--is a function that prevents hotlinking.

Although the return value of the function is Boolean, the PHP engine is compiled with a composite view, so the Submitcheck (' islogin ') = = ' Yes ' can run, but it should not achieve the desired effect.

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