What kind of caching? The $ is just part of the variable name and afaik has no special meaning.
Personally, I use $ to denote function parameters. It looks a little strange at first, however I received positive feedback from my colleagues, since it makes it easier to keep track of what is assigned to what.
// for example, assigning a new value to an input parameter
// is really bad, however easy to detect because of the notation
function foo($bar, $baz) {
// don't do the following
// $bar += 1;
// instead create a new local variable
const myBar = $bar + 1;
// because someone else might have to extend the function
// further down and doesn't see that you changed the parameter
// so, in the long run, you can prevent bugs and extra time
doSthElse($bar, myBar);
}
^personal experience. I once changed a parameter and two years later had to debug the code, because my additional code seemed correct, but it would just not work.