PHP 函数按作用域如何分类？

function sum($num1, $num2) {
  $result = $num1 + $num2;
  return $result;
}

$result = sum(10, 20); // 输出：30

$global_var = 10;

function changeGlobalVariable() {
  global $global_var;
  $global_var = $global_var + 1;
}

changeGlobalVariable();
echo $global_var; // 输出：11

function incrementStaticVariable() {
  static $static_var = 0;
  $static_var++;
  return $static_var;
}

echo incrementStaticVariable(); // 输出：1
echo incrementStaticVariable(); // 输出：2

function testScope() {
  $local_var = "Local Value";

  global $global_var;
  $global_var = "Global Value";

  static $static_var = "Static Value";

  echo "Local Variable: $local_var<br>";
  echo "Global Variable: $global_var<br>";
  echo "Static Variable: $static_var<br>";
}

testScope();

echo "<br>";

testScope();

Local Variable: Local Value
Global Variable: Global Value
Static Variable: Static Value

Local Variable: Local Value
Global Variable: Global Value
Static Variable: Static Value 2