Mhm.
That usage of "synchronous" and "asynchronous" seems to me (who uses these terms predominantly in conjunction with parallel algorithms) "weird". So, an explanation that connects the terms with the (my?) "standard" meaning would be nice; if this is too hard, just telling "There are also asynchronous stream ciphers, which don't do a simple after-the-key-stream-creation combining, but mix the key with the plaintext in one big machine. This book will only deal with the more "modular" synchronous stream ciphers" or the like would be nice.