Read anything
that has rules in it.

use Phplrt\Parser\Exception\UnexpectedTokenException;
use Phplrt\Source\VirtualFile;

try {
    $parser->parse(new VirtualFile('filter.txt', $input));
} catch (UnexpectedTokenException $e) {
    echo $e->getMessage();  // the sentence
    echo $e;                // …and the block above

    $e->token->name;    // T_AND
    $e->token->offset;  // 23
}

use Phplrt\Contracts\Lexer\Channel;
use Phplrt\Exception\ErrorPrinter;
use Phplrt\Exception\Printer\Level;

foreach ($lexer->lex($source) as $token) {
    if ($token->channel !== Channel::Unknown) {
        continue;
    }

    echo new ErrorPrinter()
        ->print($source, $token->offset, $token->size)
        ->withMessage('Unrecognized input, skipped')
        ->withLevel(Level::Warning)
        ->withLinesAround(0);
}

final class FieldException extends \RuntimeException
{
    public function __construct(
        string $message,
        public readonly ReadableInterface $source,
        public readonly int $offset,
        public readonly int $length = 0,
    ) {
        parent::__construct($message);
    }

    public function __toString(): string
    {
        return (string) new ErrorPrinter()
            ->print($this->source, $this->offset, $this->length)
            ->withMessage($this->getMessage())
            ->withClass(static::class);
    }
}

use Phplrt\Parser\Analysis\Mode;
use Phplrt\Parser\Analysis\Result\SuccessfulResult;

$result = $parser->analyze($source);

// SuccessfulResult · PartialResult · FailureResult
$result->value;          // what the fragment reduced to
$result->token->offset;  // where it stopped
$result->diagnostics;    // and what stood in the way

// greedy rules tell "not finished" from "written wrong" —
// which is exactly what a search box needs
if ($parser->analyze($typed, Mode::SyntaxCheck)
    instanceof SuccessfulResult) {
    $button->enable();
}