Phan\Language\Element\Variable::isSuperglobalVariableWithName PHP Method

    public static function isSuperglobalVariableWithName(string $name) : bool
    {
        if (array_key_exists($name, self::_BUILTIN_SUPERGLOBAL_TYPES)) {
            return true;
        }
        return in_array($name, Config::get()->runkit_superglobals);
    }

 /**
  * Visit a node with kind `\ast\AST_VAR`
  *
  * @param Node $node
  * A node of the type indicated by the method name that we'd
  * like to figure out the type that it produces.
  *
  * @return UnionType
  * The set of types that are possibly produced by the
  * given node
  */
 public function visitVar(Node $node) : UnionType
 {
     // $$var or ${...} (whose idea was that anyway?)
     if ($node->children['name'] instanceof Node && ($node->children['name']->kind == \ast\AST_VAR || $node->children['name']->kind == \ast\AST_BINARY_OP)) {
         return MixedType::instance()->asUnionType();
     }
     // This is nonsense. Give up.
     if ($node->children['name'] instanceof Node) {
         return new UnionType();
     }
     $variable_name = $node->children['name'];
     if (!$this->context->getScope()->hasVariableWithName($variable_name)) {
         if (!Variable::isSuperglobalVariableWithName($variable_name)) {
             Log::err(Log::EVAR, "Variable \${$variable_name} is not defined", $this->context->getFile(), $node->lineno ?? 0);
         }
     } else {
         $variable = $this->context->getScope()->getVariableWithName($variable_name);
         return $variable->getUnionType();
     }
     return new UnionType();
 }