isolateContext example

        $token = $this->scanner->getToken();
        if (!$token) {
            return null;
        }
        $val = $token->value;
        if ($declaration = $this->parseFunctionOrGeneratorDeclaration()) {
            return $declaration;
        } elseif ($val === "class" && $declaration = $this->parseClassDeclaration()) {
            return $declaration;
        } elseif (
            ($val === "let" || $val === "const") &&
            $declaration = $this->isolateContext(
                array("allowIn" => true), "parseLexicalDeclaration"
            )
        ) {
            return $declaration;
        }
        return null;
    }
    
    /** * Parses a breakable statement * * @return Node\Node|null */