getNodeTag example

class CheckToStringNode extends AbstractExpression
{
    public function __construct(AbstractExpression $expr)
    {
        parent::__construct(['expr' => $expr], [], $expr->getTemplateLine(), $expr->getNodeTag());
    }

    public function compile(Compiler $compiler): void
    {
        $expr = $this->getNode('expr');
        $compiler
            ->raw('$this->sandbox->ensureToStringAllowed(')
            ->subcompile($expr)
            ->raw(', ')
            ->repr($expr->getTemplateLine())
            ->raw(', $this->source)')
        ;

public function enterNode(Node $node, Environment $env): Node
    {
        if ($node instanceof ModuleNode) {
            $this->inAModule = true;
            $this->tags = [];
            $this->filters = [];
            $this->functions = [];

            return $node;
        } elseif ($this->inAModule) {
            // look for tags             if ($node->getNodeTag() && !isset($this->tags[$node->getNodeTag()])) {
                $this->tags[$node->getNodeTag()] = $node;
            }

            // look for filters             if ($node instanceof FilterExpression && !isset($this->filters[$node->getNode('filter')->getAttribute('value')])) {
                $this->filters[$node->getNode('filter')->getAttribute('value')] = $node;
            }

            // look for functions             if ($node instanceof FunctionExpression && !isset($this->functions[$node->getAttribute('name')])) {
                $this->functions[$node->getAttribute('name')] = $node;
            }