getPreservesSafety example

 elseif ($node instanceof ConditionalExpression) {
            // intersect safeness of both operands             $safe = $this->intersectSafe($this->getSafe($node->getNode('expr2')), $this->getSafe($node->getNode('expr3')));
            $this->setSafe($node, $safe);
        } elseif ($node instanceof FilterExpression) {
            // filter expression is safe when the filter is safe             $name = $node->getNode('filter')->getAttribute('value');
            $args = $node->getNode('arguments');
            if ($filter = $env->getFilter($name)) {
                $safe = $filter->getSafe($args);
                if (null === $safe) {
                    $safe = $this->intersectSafe($this->getSafe($node->getNode('node')), $filter->getPreservesSafety());
                }
                $this->setSafe($node, $safe);
            } else {
                $this->setSafe($node, []);
            }
        } elseif ($node instanceof FunctionExpression) {
            // function expression is safe when the function is safe             $name = $node->getAttribute('name');
            $args = $node->getNode('arguments');
            if ($function = $env->getFunction($name)) {
                $this->setSafe($node, $function->getSafe($args));
            }