Write a grammar,
get a parser.

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

try {
    $parser->parse(VirtualSource::createFromString(
        'filter.txt',
        $input,
    ));
} catch (UnexpectedTokenException $e) {
    echo $e->getMessage();  // just the message
    echo $e;                // the whole 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\PartialResult;
use Phplrt\Parser\Analysis\Result\SuccessfulResult;

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

// SuccessfulResult · PartialResult · FailureResult
$result->value;               // what it reduced to

// a source read in full has nothing more to say
if ($result instanceof PartialResult) {
    $result->token->offset;  // where it stopped
    $result->error;           // what stood in the way
}

// greedy rules separate "not finished yet" from
// "written wrong", which is what a search box needs
$check = $parser->analyze($typed, Mode::SyntaxCheck);

if ($check instanceof SuccessfulResult
    && !$check instanceof PartialResult) {
    $button->enable();
}