What are the valid characters in PHP variable, method, class, etc names?

Question

What are the valid characters you can use in PHP names for variables, constants, functions, methods, classes, ...?

The manual has some mentions of the regular expres

Answer 1

NikiC has all of them except functions. With variable functions you can have whatever name you want, though the syntax sucks.

${'=^^='}=function(){
   echo "Hello Kitty!";
};

${'=^^='}(); //outputs "Hello Kitty!"