Functions don't need to be defined before they are called. In this example, function

printMe()

is defined after it's called but it works without errors

echo printMe();

function printMe() {
    return 'Print some text';
}

Exception is

conditional function

. In this example function

foo()

will not be defined until the

if ($makefoo)

conditional statement gets executed

$makefoo = true;

/* We can't call foo() from here 
   since it doesn't exist yet,
   but we can call bar() */
// foo();

bar();

if ($makefoo) {
  function foo()
  {
    echo "I don't exist until program execution reaches me.\n";
  }
}

/* Now we can safely call foo()
   since $makefoo evaluated to true */

if ($makefoo) foo();

function bar() 
{
  echo "I exist immediately upon program start.\n";
}

Functions within functions. Function

bar()

will not be defined until the function

foo()

is executed

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

/* We can't call bar() yet
   since it doesn't exist. */
// bar();


foo();

/* Now we can call bar(),
   foo()'s processing has
   made it accessible. */

bar();

Note: All functions in PHP have the global scope - they can be called outside a function even if they were defined inside and vice versa