Revision: Sat, 01 Aug 2020 19:23:52 GMT

Stempler - AST Modifications

Stempler template engine fully exposes template AST (DOM) and provides API for the modifications similar to

You can create magical (in both ways) workflows and helpers by implementing your Node Visitors.

You can read more about how traversing works here.

Create Visitor

To create an AST visitor, you must implement interface provided by the Stempler engine - Spiral\Stempler\VisitorInterface.

We will try to create visitor which automatically adds alt attribute to all img tags found in your templates:

use Spiral\Stempler\Node\HTML;
use Spiral\Stempler\VisitorContext;
use Spiral\Stempler\VisitorInterface;

class AltImageVisitor implements VisitorInterface
    public function enterNode($node, VisitorContext $ctx)

    public function leaveNode($node, VisitorContext $ctx)
        if ($node instanceof HTML\Tag && $node->name === 'img') {
            $alt = null;
            foreach ($node->attrs as $attr) {
                if ($attr->name === 'alt') {
                    $alt = $attr;

            if ($alt === null) {
                $node->attrs[] = new HTML\Attr('alt', '"this is image alt"');

You can inject other tags or even PHP into your templates.

Register Visitor

Call StemplerBootloader->addVistitor to register visitors in the template engine. We can do it using application bootloader:

namespace App\Bootloader;

use App\Visitor\AltImageVisitor;
use Spiral\Boot\Bootloader\Bootloader;
use Spiral\Stempler\Bootloader\StemplerBootloader;

class AltImageBootloader extends Bootloader
    public function boot(StemplerBootloader $stempler)

You have to clean view cache to view newly applied changes.

Now all the img tags will always include alt attribute.

Standalone Usage

You can use the Stempler to process any HTML content.

use Spiral\Stempler;

$parser = new Stempler\Parser();
    new Stempler\Lexer\Grammar\HTMLGrammar(), 
    new Stempler\Parser\Syntax\HTMLSyntax()

$template = $parser->parse(new Stempler\Lexer\StringStream("<BODY>content</BODY>"));

$traverser = new Stempler\Traverser();
$traverser->addVisitor(new CustomVisitor());

$template->nodes = $traverser->traverse($template->nodes);

$compiler = new Stempler\Compiler();
$compiler->addRenderer(new Stempler\Compiler\Renderer\CoreRenderer());
$compiler->addRenderer(new Stempler\Compiler\Renderer\HTMLRenderer());

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