Any valid PHP code may appear inside a function even other function and class definitions.
The function name must start with any letter or underscore followed by digits, letters, underscores. They are case insensitive.
Funcs need not to be defined before they are referenced, except when a function is conditionally defined.
PHP does not support function overloadind, nor it is possible to undefine or redifine previously-declared functions.
func_num_args() , func_get_arg() , func_get_args()
All functions and classes have the global scope.
It is possible to call recursive functions

function foo(){
   function bar(){
      echo "I don't exist until foo() is called. \n";    
   }
}


function recursion($a){
   if($a < 20){
      echo "$a\n";
      recursion($a+1);
   }
}

Continue reading “PHP functions mini guide”