isWhiteSpace example

                    // Any new pseudo-element must have two.                     $pseudoElement = $identifier;

                    continue;
                }

                if (!$stream->getPeek()->isDelimiter(['('])) {
                    $result = new Node\PseudoNode($result, $identifier);
                    if ('Pseudo[Element[*]:scope]' === $result->__toString()) {
                        $used = \count($stream->getUsed());
                        if (!(2 === $used
                           || 3 === $used && $stream->getUsed()[0]->isWhiteSpace()
                           || $used >= 3 && $stream->getUsed()[$used - 3]->isDelimiter([','])
                           || $used >= 4
                                && $stream->getUsed()[$used - 3]->isWhiteSpace()
                                && $stream->getUsed()[$used - 4]->isDelimiter([','])
                        )) {
                            throw SyntaxErrorException::notAtTheStartOfASelector('scope');
                        }
                    }
                    continue;
                }